Catalog updates

[boyswan]

Currently it's not possible to access Catalog modules without manually depending on the rmrk_catalog crate. This breaks the current convention of the single rmrk crate entrypoint.

This PR exposes the catalog modules via the rmrk entrypoint crate, and updates the catalog_example dependencies.

Other fixes:

• Handle invalid utf8 metadata with RmrkError instead of empty string
• Fallible constructor in catalog_example

[Maar-io]

Two observations.

Main idea with Catolog being separate contract is re-usability of the Catalog contract., as well as lowering the contract size. Wouldn't this change include Catalog in every contract?

Many functions names are changed in this PR. The naming of the functions was a copy the EVM version.

[boyswan]

Main idea with Catolog being separate contract is re-usability of the Catalog contract., as well as lowering the contract size. Wouldn't this change include Catalog in every contract?

So the Catalog will still be used as a separate contract and this shouldn't effect the size due to dead code elimination at compile time. The size of the final contract will be determined by the amount of code that is actually used from rmrk, not everything that's available in the lib.

For example if we have a contract that only implements the Minting trait, the Nesting/Equippable/etc impls will not be included in the compiled contract. This will be the same for the catalog - only the Catalog impl will contribute towards the final size.