Update dependencies and use near-plugins

[mfornet]

Use near-plugins to extend contracts with new functionalities.

1. Ownable pattern allows setting the owner to a DAO that can control admin functions from the bridge.
2. Pausable changes the old mechanism for pausing functions, but provides the same features.
3. Upgradable allows owner to upgrade the bridge to a new version.
4. FullAccessKeyFallback allows the owner to attach a full access key in case of Emergency.

Notes for reviewer:

Check notes from reviewer here: Near-One/rainbow-bridge#714

Testing plan

• All bridge tests should pass, i.e. basic mechanisms of the bridge haven't changed.
• WIP: Add tests to check all new features works as expected