Support upgrading clients to new applicationconfig

[awillersrud]

Support for multiple ApplicationConfig for each Application. One needs to be marked as default.

autoUpgrade flag per client for controlling which clients should be upgraded. Flag is already present, although not used for anything yet.

Reverse the mapping from application -> config in PersistedConfigRepo, existing map can be used to mark default config.

Change GET /application/{id}/config to return applicationconfig's just for the given application. Currently it returns applicationconfig's for all applications as there is no link between applicationconfig and application.