Phoebe refactor

The whole data layer has been refactored. No more Global Model Lock :tm:. Both Joey and iOS build and run again. Closes #195.

Also fixes various issues that couldn't have been fixed before:
- Project list composing uses direct SQL statement and optimised querying. Closes #188.
- It should be now quite impossible to have multiple running timers. Closes #159.
- Probably fixes #124, where deletions aren't synced.
- Time entry tags are now correctly synced from server. Closes #22.