Move Predefined Tags sync business logic to MigrationService

[epugh]

This is to fix #89 by leveraging the fact that the MigrationService already is checking if Evolutions have been completed and making decisions. So we move some of the logic over to it.

I move the FeatureToggle check into the MigrationService, though not sure if that was the right way to go...

Now SMUI will start with an empty Database, run the Evolutions, and then when you restart, sync any predefined tags.

[epugh]

There was some discussion on Stack overflow about lazy loading things in Play frameworks, so this issue might go away if we are on a newer Play framework.

[pbartusch]

Hi @epugh , thanks for the PR and for finding this bug.
I moved the whole routine for synch'ing the predefinedTags to the migrationService and removed it from the repository. It's different in nature, as it is nothing being used during the end user runtime of SMUI. It should not have been in the repository, in the first place.