modbus_plugin: generate nicer error message, instead of a traceback

Modbus plugin: Add "exec. req. flag" and "write on change" features

PLCObject : reorganize code in StartPLC(), add a PreStartPLC() empty method, to be overloaded by runtime extensions.

Solve import order problem when POULibrary imports ConfigTreeNode because of UserAddressedException. Now UserAddressedException is declared in POULibrary.py, as a quick and dirty fix, but some independant module should be created for beremiz exceptions in general.

Add --on-plc-start --on-plc-stop and --status-change to runtime command line, calling given command respectively on start stop or any event. Command line string is python formated (to eventually include status with {}) before being split (supports quoted strings) and passed to Popen for non-blocking execution.

Etherlab : Merged 2014-2018 changes from jblee and others

Close branch ethercat_from_kosmos

EtherCat master plugin : commit changes recovered from KOSMOS 2018 installer, unkown author(s).

Add FatalError() method to ConfigTreeNode.
Extensions can report error addressed to user, without a traceback.

Fixed one more sequel of marking temporary variables created while generating ST code out of FBD

Changed yslt_noindent.yml2 again

Non significant changes in generated xslt, side effect of changes in yslt_noindent.yml2

More customizations to yslt

PLCobject: Call "stop" and "cleanup" methods from python runtime files in reverse order compared to "init" and "start".

Non significant changes to mute GCC warnings about unused variables.

Fixed sequel of earlier commit in PLCGenerator.py. Some ref to temporary variables are still not using the _TMP_ prefix. They are quite hard to find, so to be continued...

variable access code moved from plc_debug.c to targets/var_access.c for easiewr re-use in ext.

Swap CTN code gen and Libraries code generation order. In general library part of an extension needs to be computed before CTN part.

yslt_noindent : Avoid YSLT's indent logic to interfere when using linequote.

Add marker to temporary variables created while generating ST code out of FBD, so that they can be recognized as such.

Allow using docutil.get_inkscape_path() on Linux also.

Moved XSLT model query python code so that XSLT part can be reused for other transformations

Fixed unitialized parameter in instances_path stylesheet, leading to
calls to add_instance with no data when passing datatypes insteatd of project
root. That bug was making exceptions (for exemple when editing type) when
having arrays of derivated types in project.

Fixed code quality according to pep8 and pylint.

Fix exception on exit in some case, sequel of an earlier cleanup commit I couldn't find back. Disconnecting the event is apparently the way to go. https://wiki.wxpython.org/Surviving%20with%20wxEVT%20KILL%20FOCUS%20under%20Microsoft%20Windows

PurgeBlobs was faulty, but it was never having anything to purge. Fixed.

Fixed repetitive freezing of IDE when connection drops.
when connection lost error was beeing displayed, the involved wxYield
was calling pending plc status periodic update, itself trying to use connector.
At that time connector is still not destroyed and connection
is attempted again when calling GetPLCStatus.
=> Hack : Ensure connector is destroyed before reporting error.

Better error handling when blob transfer fail

Removed dead code.

Now expects 1 more columns in VARIABLE.CSV file generated by MatIEC. Pair with MatIEC commit 9cb7c8bf7dbc :
Add a column to VARIABLES.CSV, containing variable (derived) type name, additionally to current last column contyaining base type name