Create ownables_utils crate

[jasny]

The ownables rust contains a lot of boilerplate code. The amount of code, even though it doesn't need to be touched, can be overwhelming for new Ownable developers.

Create an ownables_utils crate and move as much common logic there.

• IdbStorage (maybe rename to ExternalStorage, because it's not dependent on indexeddb)
• address_eip155 and address_lto
• Common structs from msg.rs and state.rs