Test RemoteId changing and cache updating.

Test that the RemoteId is correctly updated by Merge and that the model
caches update their indices with new data as well.
Fix cache updating bug introduced by previous refactor.

When refactoring model lookup code into ModelManager (b87aaed), a subtle
bug was introduced where looking up the cache for a model failed. This
simple typo is now fixed with added unit tests (2c34ee4) to make sure
this wouldn't happen in the future.
Test time entry model.

Add some tests for TimeEntryModel to validate the business logic in it.
Fix not setting stop time when stopping time entry.

Time entry tests (from 1e50d08) revealed that the StopTime was not being
correctly set when the time entry was stopped.
Merge branch 'master' into alex-ui
Make project color handling simpler