Fix compilation warning/error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]

merge

WxGlade HMI extension now does only instanciate wx object who's name match extension's name. If no object match the name and no code is provided in 'start' user python code section, then a warning is issued

BACnet : ensure that Init did happen before continuing with PLC startup.

Update list of files with strings for i18n and templates for translations

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