Video support

Created by: retiolus

App doesn't let to select mp4 files or other video format to edit/publish

Multiple aspects to add video support:

• Make videos show up in the feed
• Upload videos (when supported by instance, see #175 (closed) for info about the /.well-known/nodeinfo endpoint)
• Edit videos before uploading (add a filter, crop, maybe trim the video, change speed?)
• Once video support is enabled, add video/* to the intent filter of the PostCreationActivity