make clipboard open minimal time as wxPython documentation recommends

https://wxpython.org/Phoenix/docs/html/wx.Clipboard.html#wx.Clipboard.GetData

"Call wx.Clipboard.Open to get ownership of the clipboard. If this
operation returns True, you now own the clipboard. Call
wx.Clipboard.SetData to put data on the clipboard, or
wx.Clipboard.GetData to retrieve data from the clipboard. Call
wx.Clipboard.Close to close the clipboard and relinquish ownership.
You should keep the clipboard open only momentarily."

Maybe it makes situation with pretty annoying error 'clipboard already
open' a little bit better.

traceback:
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/BeremizIDE.py", line 955, in OnSaveProjectMenu
self.RefreshAfterSave()
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/BeremizIDE.py", line 946, in RefreshAfterSave
self._Refresh(TITLE, FILEMENU, EDITMENU, PAGETITLES)
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/IDEFrame.py", line 926, in _Refresh
self.RefreshFunctions[element]()
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/BeremizIDE.py", line 766, in RefreshEditMenu
IDEFrame.RefreshEditMenu(self)
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/IDEFrame.py", line 1185, in RefreshEditMenu
if self.GetCopyBuffer() is not None:
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/IDEFrame.py", line 956, in GetCopyBuffer
if wx.TheClipboard.Open():
File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk3/wx/_misc.py", line 5793, in Open
return _misc_.Clipboard_Open(*args, **kwargs)
<class 'wx._core.PyAssertionError'>: C++ assertion "!m_open" failed at ../src/gtk/clipbrd.cpp(598) in Open(): clipboard already open

Merged GPL + LGPL v2 or later EtherCAT extension. Fixed headers and copyright notice.

Propagated matiec changes in FB var accessors

Fixed most obvious bugs appear after grafting changes from previous development branches : re-enable openning non-CoE, CoE and CiA 402 nodes config

Fixed xslt stylesheet for extracting entries defined in module, rewiting xslt stylesheet to yslt

Fixed bug in information returned for module where entries are defined only in PDO mapping

Added support for loading XML file even if not following XSD schema (but still following XML syntax), warning user of errors in XML file

Fixed bug when compiling

Fixed higen example removing obsolete attribute in CIA402 node params file

Fixed controllers for working with latest version of xmlclass

Added bug in support for set flag for optional variables activation in axis public struct

Added support for set flag for optional variables activation in axis public struct

Replaced location for axis ref from %IW(location).0 to %IW(location).402. Added location for network position at %IW(location).

Rewrite CIA402 node specific code generating part

Cherry-pick and re-commit to legitimate ancestor of commit 'Ethercat Management Function Refactoring Source by RTES Lab.' from youcu <youcu1022@gmail.com>

Fixed bug when drag'n dropping variable in master startup command grid

Moved ratio scaling back to MCL. Rewrote CiA402 C part in a way it can be read and understood by some humans.

Added icon for Ethercat extension root and Ethercat master node

Fixed bug with global instance declaration

Fix bug in when moving Ethercat slaves fixed

Added mapping for TouchProbe function in CIA402 slave node

Fixed bug with axes boolean parameters value

Added error message when a device informations can't be found in ESI files

Fixed ToolTip on VariablesGrid columns on Windows

Update higen drive example introducing usage of csv mode

Merged

Fixed bug in support for module extra params in EthercatCFileGenerator

Added support for module extra params in EthercatCFileGenerator

Fixed support for multiple module extra params in ModulesLibrary

Added support for multiple module extra params in ModulesLibrary