Add small contributing document with information about codestyle checking

Add argument to set list of source files to check

This is necessary, in case you want to use docker run in pretxncommit
Mercurial hook. Unfortunately for some reason if hg running in
container can't find just created commit defined by $HG_NODE. And it
throws error 'unknown revision'.

Here is example for hgrc.

[hooks]
pretxncommit.linter = hg status -m -n -a -n -I '**.py' --change $HG_NODE > files.lst && docker run --volume=$PWD:/beremiz --workdir="/beremiz" --volume=$PWD/../CanFestival-3:/CanFestival-3 --memory=1g --entrypoint=/beremiz/tests/tools/check_source.sh skvorl/beremiz-requirements --files-to-check files.lst

check_source.sh: handle case if there are no files to check

Fix linter errors

Add command line argument to run linter only on changed files

./tests/tools/check_source.sh --only-changes

It's recommended to run check_source.sh automatically on each commit,
so the rules are always enforced.
Even better is to use docker for that, so the versions of pep8 and
pylint are the same as on pipeline server.

To do this couple of lines should be added into repository's hgrc file.

[----------- cut from .hg/hgrc------------------]

[hooks]
precommit.linter = ./tests/tools/check_source.sh --only-changes
# precommit.linter = docker run -it --volume=$PWD:/beremiz --workdir="/beremiz" --volume=$PWD/../CanFestival-3:/CanFestival-3 --memory=1g --entrypoint=/beremiz/tests/tools/check_source.sh skvorl/beremiz-requirements --only-changes

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Don't use fixed width labels in WAMP and PYRO dialogs

This causes problems if labels are translated into other languages and
width wasn't enough.

Fix internatialization in UriLocationEditor, PYRO dialog and Modbus configurator

Add copyright headers to retain implementation for GNU/Linux and Win32

Drop support for wxPython 2.6 and below

Autoresize UriLocationEditor dialog window