Fix 'DoGetTextExtent - invalid DC' error

most likely this error happens only on certain wx backends.
GTK3+ on GNU/Linux is apparently one of them.
The problem is described in wxWidgets issue tracker.
http://trac.wxwidgets.org/ticket/12486

[-------------------------------------------------------------------------------------------------------------------]
platform:
Linux-4.16.0-2-rt-amd64-x86_64-with-debian-buster-sid

python-version:
2.7.15

traceback:
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 1605, in DispatchDebugValuesProc
self.CallWeakcallables("__tick__", "NewDataAvailable", debug_ticks)
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 1585, in CallWeakcallables
function(*cargs)
File "/home/developer/WorkData/PLC/beremiz/beremiz/editors/Viewer.py", line 1217, in NewDataAvailable
refresh_rect.Union(element.GetRedrawRect())
File "/home/developer/WorkData/PLC/beremiz/beremiz/graphics/GraphicCommons.py", line 1609, in GetRedrawRect
self.ValueSize = self.Parent.GetMiniTextExtent(self.ComputedValue)
File "/home/developer/WorkData/PLC/beremiz/beremiz/editors/Viewer.py", line 932, in GetMiniTextExtent
return self.MiniTextDC.GetTextExtent(text)
File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk3/wx/_gdi.py", line 4127, in GetTextExtent
return _gdi_.DC_GetTextExtent(*args, **kwargs)
<class 'wx._core.PyAssertionError'>: C++ assertion "m_graphicContext" failed at ../src/common/dcgraph.cpp(1160) in DoGetTextExtent(): wxGCDC(cg)::DoGetTextExtent - invalid DC

wx-platform:
__WXGTK__

wx-version:
3.0.2.0

[-------------------------------------------------------------------------------------------------------------------]

traceback:
File "/home/developer/WorkData/PLC/beremiz/beremiz/controls/LogViewer.py", line 740, in OnMessageToolTipTimer
self.MessageToolTip.SetFont(self.Font)
File "/home/developer/WorkData/PLC/beremiz/beremiz/controls/CustomToolTip.py", line 75, in SetFont
self.RefreshTip()
File "/home/developer/WorkData/PLC/beremiz/beremiz/controls/CustomToolTip.py", line 158, in RefreshTip
self.SetClientSize(self.GetToolTipSize())
File "/home/developer/WorkData/PLC/beremiz/beremiz/controls/CustomToolTip.py", line 145, in GetToolTipSize
w, h = dc.GetTextExtent(line)
File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk3/wx/_gdi.py", line 4127, in GetTextExtent
return _gdi_.DC_GetTextExtent(*args, **kwargs)
<class 'wx._core.PyAssertionError'>: C++ assertion "m_graphicContext" failed at ../src/common/dcgraph.cpp(1160) in DoGetTextExtent(): wxGCDC(cg)::DoGetTextExtent - invalid DC

[-------------------------------------------------------------------------------------------------------------------]

Fix size of ProjectDialog used by PLCOpenEditor

Disable scrolling for ProjectDialog, because otherwise very very small
windows is created.
This regression was introduced by 5701225 ("replaced normal panel with scrolled panel under project
properties").

Fix some compilation warnings for better ANSI C compliance

Customizable columns in VariableTables (i.e. can be monkey patched properly)

Merged

Customizable update of toolbar buttons (i.e. 'methods') according to PLCStatus

Fixed small typo in error message.

WAMP : complains about failure to start WAMP only if it was successfully imported.

WAMP: now config and secret given in project files always override those given in commandline. Also made extensions web customisations happen before registration of web interface.

Moved Wamp configuration file selection logic into runtime/wampclient.py. Added Wamp CRA secret file upload and download. Slightly reworked code for config and secret file loading and saving.

Added a way for extension to register dedicated URL under settings page URL (i.e. /settings/something)

Fixed a bit of everything in WAMP, and added web settings for that same extension.

Added some immutable field (platform) in default runtime web setting page, for the example.

Fix misc typos in exception handling code.

Fixed i18n related typo.

Fixed typo

Better logging of Nevow Server import in case of exception.

WampClient : Simplified, removed dead code, use exception for handling failures and misconfiguration, check existence of mandatory parameters.

Merged #2486, enhancements to WAMP client : auto reconnecting, wamp conf checking and saving, additional attributes for exposed calls, etc

Nevow based web interface now show simple Log message sending form for basic runtime, and allow extensions to add their own web settings.

Now, runtime extensions should be able to add their own settings to web configuration interface.

Embrio of setting form, just to test

#2486 Exception if custom protocol options are wrong.

#2486 ExposedCalls with register options as a dictionary.

#2486 Renaming functions.

#2486 Reconnect funtion in SaveWampClientConf function.

#2486 Modified reconnect function. Added 'active' parameter to wampconf.json file.

#2486 Adding reconnect funtion to WampClient. Global TransportFactory not needed anymore.