Mock database persistence

[B3rn475]

At the moment the mock database in the generated/emulated code is not persisted.
After each run of the code generator it is restored to the default value.

It could be interesting to store the latest version of the database and preserve it after a model change.

Open questions:

1. Where should i store the database? (metadata field of the model?)
2. Could be interesting to edit the database from the model editor?
3. How can i share the database between the emulators? (check if they are consistent)
4. If I'm sharing the database between the emulators, how should I manage out of sync code?