dogtail: Remove testing of missing font chooser element
timeline: Remove previous/next keyframe menu items

The logic is missing and we are not sure how useful they are.
The unittests when the functionality has been added are long gone:
efa26eb0
timeline: Clarify a fixme
timeline: Cleanup the logic which allocates a ghostclip to a layer
timeline: Fix dragging an asset to the ruler

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1061824
Use the soft dependencies objects from the check module
project: Avoid emitting done-importing when a title asset is added

When creating a new project and clicking Title > Create-and-insert,
the project emits done-importing which should be signalled only when
importing external files.