code checker flake8 as alternative / extension to pyflakes added

first commit to rework the syntax checking of scripts with the goal to support pyflakes and / or flake8

first demo version of flake8 checker

new icons for syntax / style check / linter warnings of info messages

property editor adapted and extended by new syntax and style checker options

typo

further work on improved code checker feature

more work on code checkers (pyflakes, flake8)

more improvements in code checkers

many improvements for the two different code checkers: pyflakes or flake8

more improvements for itomSyntaxCheck.py module

documentation adapted for new code checkers

documentation improved

auto mode for codeCheckers added

docs improved