room-history: Improve sending attachments
- Use a common widget for viewing media content in the media viewer and the attachment dialog, which means videos and audio clips can be also be previewed before sending.
- Clean up clipboard and drag-n-drop sending.
- Preview the location to send with the attachment dialog.
Fixes Crash on paste (#992 - closed).
@afranke there are new strings.
Edited by Kévin Commaille