Add timeline for project & files

[FinnWoelm]

We want to able to display a history of a file's versions, eg:

ID	FileInBranch	Version	Action	Actors
1	1	1	:create	[1]
2	1	2	:update	[2, 3]
3	1	1	:restore	[1]

Open Questions:

• What actions should we track?
• What information should we track?
• How do we avoid redundancy with FileInBranch's current_version_id and committed_version_id?
• How do we handle branch merges?