Fixes some issues with inline images.

fixes #214

Limiting improves readability on wide monitors.

The immediate update of the settings is done by just exposing settings
as properties and then setting the settings as a context property.

Messages on /sync don't have a room_id

(This is such a hack and will probably break, but it works for now for
most cases...)

This is necessary to support having a picker within QML.
Eventually, this should replace the existing widget-based one.

closes #94