Change imports to use absolute paths
[WebUI] Replace func_globals with __globals__ for Py3 compat
[WebUI] Add reduce import for Py3 compat
[Plugins] Fix relative imports to use dot notation
Remove gtkui specific func from path_chooser_common
[Tests] Replace module import with sys.modules
Add workarounds for isort

 * Add workaround for unicodedata issue
 * Change line length to 120
 * Skip gtkui.py to stop it moving local imports above the install reactor line
Flake8 pass of entire codebase

 * Use the inline '# NOQA' to supress N802 lower-case warnings
Update with new license header