Add custom dialog to add/edit comment block in graphical editors

That allows to edit comment and immediately see how it'll be shown on wiresheet.

Cleanup examples so they look clean, nice and almost the same on Windows and GNU/Linux

use the same font size on Windows and GNU/Linux

use nice and pretty mono font in graphical languages (SFC, FBD, LD) as well

it looks like that was original idea, but some bug squashed in and
default font was used for POU.

at the same time fix use of mono font in the header of Variable panel
for SFC/FBD/LD POUs.

Don't need to call extra _init_

_init_ is already called for value in infos["elmt_type"]["initial"]().
Additional _init_() creates second set of child element and that
creates unusable xml project.
This regression cause by not well tested commit "Proper fix for error
'object has no attribute 'getSlave' in EtherCAT extension" (96ca6b056c55595f71bfaca9f54b9e8646460c23)

Fix black background in preview window

Problem found and fixed on GNU/Linux
wxWidgets 3.0 built with GTK3+ support and running on Xorg.

Avoid division by zero in case width or height for page are not specified

traceback:
File "/home/developer/WorkData/PLC/beremiz/beremiz/editors/Viewer.py", line 3755, in OnPaint
self.DoDrawing(dc)
File "/home/developer/WorkData/PLC/beremiz/beremiz/editors/Viewer.py", line 3723, in DoDrawing
for y in xrange(self.PageSize[1] - (ystart * SCROLLBAR_UNIT) % self.PageSize[1], int(window_size[1] / self.ViewScale[1]), self.PageSize[1]):
<type 'exceptions.ZeroDivisionError'>: integer division or modulo by zero

IDManager: added import/export plus little cosmetic enhancements.

IDManager : refactored a bit, moved some code into PSKManagement.py. Now captures URI and PSK on new PYRO(S) and propose them when editing URI. Import/export still to be implemented.

Renaming servicetype into scheme.

Added toolbar button to launch ID Manager dialog.

Renamed IDManager control into IDBrowser, because dialog will be named IDManager

IDManager.py : finished selector mode.

Added early implementation of IDManager.py. For now only used to select ID in URIEditor

Path may contain spaces... sequel of d1359cb

'Merged' URI editor dialog and Discovery dialog, also clean up related code

Cut more useless code from URI Editor

URI Editor Dialog : moved it to /dialog, and fixed naming.

URI editor : Rewrote most of it, cleaner.

PSK : Stunnel and/or OpenSSL (undocumented) handles PSK better without special chars, apparently

Prevent PLCObject to be imported from IDE as a side effect of importing runtime package

WAMP : ensure that unicode string is passed for published events IDs

PYRO PSK: adjusted cipher and key length to be usable with openSSL 1.0.2k.

Automatically get PSK and ID when connecting to PYRO[S], so that future connection through PYROS can use that same key. Also fixed case to UPPER for *PSK.