Bare functionality of the widget layer restored
Port AddWidgetDialog to gtk3
Fix melange/gui.py
Remove hotkeys, record and httpserver for now
Implement a few features:

- Adding widgets is now possible through the dialog
- Moving widgets
- Removing and raising widgets
Add support for /common files
Remove config for now
Don't use relative urls for stylesheet imports
Remove dead code
Move position to widget
Implement reloading
Show layer
Use load_uri instead of open and connect signal later
Remove default parameter
Comment stuff out, things are not working, argh
Refactor WidgetLayer methods
Implement melange config and reloading on theme change
Implement widget config
Switch from single Window to a multi window approach

Instead of managing the widgets inside one big Window have

- One big Window to capture button press events to show melange
  specific dialogs
- One widget sized toplevel window per widget.

This solution is mostly necessary due to segfaults in the single window
implementation
Refactor theme handling into own class