Remove footgun around session keys/handlers (#3949)

* Remove footgun around session keys/handlers

- `OpaqueKeys` now has an associated type `KeyTypeIdProviders`. This can
be used in the runtime as input for `SessionHandler` from the session
trait.
- `impl_opaque_keys` now works with modules and extracts the `KeyTypeId`
from the module directly.
- Added some checks to the `session` storage initialization that checks
that the `SessionHandler` and `Keys` use the same number of keys and
that the order is equal.

* Update core/sr-primitives/src/traits.rs

substrate/core/application-crypto/src/traits.rs

@@ -127,3 +127,8 @@ pub trait RuntimeAppPublic: Sized  {
 	fn verify<M: AsRef<[u8]>>(&self, msg: &M, signature: &Self::Signature) -> bool;
 }
 
+/// Something that bound to a fixed `RuntimeAppPublic`.
+pub trait BoundToRuntimeAppPublic {
+	/// The `RuntimeAppPublic` this type is bound to.
+	type Public: RuntimeAppPublic;
+}