feat: Promote NsRecord into a core object

[jsantell]

... by extending noosphere_core::data::LinkRecord with its functionality, and removing the noosphere_ns dependency on validating records. Fixes #395

[cdata]

This mostly looks good.

One thing that stood out to me is that all of LinkRecord's implementation is static in order to work around the fact that what it really wants to be operating on is a Ucan (but what it has available is an encoded Jwt).

It seems like there are two possible revisions to this change that are worth choosing from:

1. Refactor LinkRecord to hold a Ucan internally (not a Jwt), or....
2. Add yet-another-wrapper that takes a LinkRecord and internally also holds a corresponding Ucan

After applying one of these approaches, the static methods can be re-imagined as instance methods without extra cost required to parse a Ucan for every call.

[jsantell]

Reconfigured to wrap a Ucan, not dissimilar from NsRecord; updating accordingly

• Promote noosphere_core::authority::generate_capability(identity: &str, action: SphereAction)
• Remove optional DidParser from LinkRecord::validate method
• Updated some traits accordingly, similar to what NsRecord needed as a Ucan wrapper (rather than a Jwt wrapper)
• Updated method names (with no static methods, dereference was redundant with link, renamed to get_link())

[cdata]

Just a little more cleanup requested 🙏

[jsantell]

updated: removed the encode() and as_bytes() methods

[cdata]

Nice work!