Add .gitignore file.
Add requirements.

This is preliminary only.
Cleanup: pep8ifying sources.

This changes have been applied to all python files using
https://github.com/htgoebel/pep8ify and the result has been checked.
Cleanup: Eliminate repeated code.
Cleanup: wrap long lines.
Fix GtkWarning: gtk_range_set_range: assertion 'min < max' failed.

Includes some clean-up.
Refactor: Use _geticon() wherever appropriate + new module _resources.
Refactor: Use loop instead of repeated calls.
Refactor duplicate code: stop/skip_forward/backward.
Wrap long line and re-indent.

I missed doing this earlier.
Cleanup: Use optparse instead of twisted.python.usage.
Cleanup: Do not test for __main__. This is always run as script.
Rearrange imports: Import twisted and upnp_inspector after arg-parsing.

Thus they get not activated if parsing the arguments fails or
usage or help is shown.
Cleanup some code.
Print traceback on error.
Cleanup.
Add shortcut for "Quit" and convert the entry into an image menu item.
Update (popup-)menu texts.

Capitalize first word, add dots where another window will open.
Adding myself as copyright holder.
Refactor: Use loop instead of repeated calls.