Add pylama to build to enforce pep8 coding standards.

As our coding guidelines state we follow pep8 we
actually should enforce that in the build.

Using default pep8 with line-length extended to 120
characters. pylama offers more linter options we might
want to enable in the future.

Linting will run before build. Build will fail if a
linting issue is found.

Linting excludes:
- src/demo
- src/tests
- Auto-generated ui and rc files

This commit will make the build fail.

Part of #1 .
Make linted code-base pep8 conformat.

Lots of trailing spaces, multiple newlines
at end of file, lambdas assigned to variables,
virtual alignment problems etc. etc.