Extensions for the AppProviders to improve the UI

[glpatcern]

This PR introduces further extensions for the open-in-app workflow:

• AppProviders expose a capability to identify fully fledged editors vs viewers
• Mime types are defined including a friendly name and a corresponding file extension

This allows the UI to e.g. populate a New menu with all types for which an editor AppProvider is defined.

The extensions constitute breaking changes for the protobuf bindings, and can be merged once cs3org/reva#2067 is ready to be merged.

[labkode]

Looks good. In general is better to not break backwards compatibility by maintaining the order of the fields in the protobuf definitions. However as this PR introduces a new REQUIRED fields it does not change anything.

@wkloucek please review and approve.

[glpatcern]

Yeah I thought about that and also about leaving them OPTIONAL (the capability at least could default to VIEWER) but in the end we need them...

[glpatcern]

Self-reviewing:

This model is still missing the ability to register the mime type attributes (name, ext, icon...) from "outside". A SetMimeType RPC method may be needed for this, but for now the implementation in Reva will populate these metadata from the config, without further needs in terms of CS3APIs.

Also, I don't understand why such a large diff in proto.lock. I dropped and recreated it as this is a breaking change, does that mean that we were carrying over lots of "garbage"?

[ishank011]

Also, you'll need to add the proto lock file for the build to pass