move all synchronization related stuff into a project's view drawer

[mpetris]

The drawer in the Project's view remains hidden as it hasn't been filled with life yet. All operations related to synchronization like

• synchronize with the team
• what of my commits haven't been synchronized yet
• what of the commits of others aren't merged into my local worktree yet

should go in that drawer.

[maltem-za]

With how central a function synchronization is in collaborative projects, there has been some discussion on whether "hiding" this functionality (especially the synchronize button itself) in the drawer is the best approach. I think we should definitely keep an obvious indication, like the current yellow bell or similar, that doesn't require you to open the drawer first.

Related: #183, #184 This should probably wait until we know the way forward on #248.