im-online: use generic crypto (#3500)

* im-online: support using ed25519 and sr25519 crypto

* app-crypto: add trait bounds to RuntimePublic::Signature

* im-online: add missing type annotations

* authority-discovery: depend on im-online module and use its crypto

* node: set i'm online crypto to sr25519

* node: bump spec_version

* rpc: don't generate i'm online pubkey in insert_key method

* im-online: fix docs

* im-online: move app crypto packages

* aura: move app crypto packages