refactor file storage to use database instead of file system

[sanderr]

One of the major complications for a high availability orchestrator is that files will be missing on failover. Putting them in the database would be a trivial way to solve that.

The goal of this ticket is to do this refactor for iso7, unless we foresee major complications for the iso6->iso7 migration as a result.

Document clearly that a compile should be triggered after the upgrade and that old files will not be migrated.