- Make Pillow the fallback loader
- Simplify loading of images
- Use Gtk.Image instead of Gajims TextViewImage

As in contacts not in our roster and contacts we are not fully
subscribed to.

- Dont depend on Gajim method, as it triggers Events that will be
shown in the chat window

- PEP is not reliable enough for now, so we have to use this as
fallback

- create a OMEMOConnection class to mimic more how Gajim does things