Logically group supported schemas by application

[sandreae]

At some point we may want to organise supported schemas into groups depending on the application they are required for. This could then be use to configure replication behaviour in a more fine grained, per-application manner. This would have an impact on on Announce, TargetSet composition and sync session establishment, our configuration flow.

For example, a fantasy config file would look like:

[[applications]]
name = "My mushroom app" # A name I give the application
schema_ids = ["sighting_0020...", "species_0020..."]
storage_allowance = 20 # MB storage allowance

[[applications]]
name = "My video sharing app"
id = ["huge_video_file_0020...", "favorite_videos_0020..."]
storage_allowance = 10000

This config would result in the node producing 2 Announce messages, and starting separate sync sessions for each set of application schema. Whether blob_v1 and blob_piece_v1 were included in each announce/target set would be different for each application and depend on their individually configured storage allowance.