Inscription titles

[casey]

• An inscription can include an additional field in the envelope header called the "title"
• The value of this field should be UTF-8 encoded text
• The title is displayed below the inscription on the /inscription page

In addition to titles, I'm thinking of using this for #943. It's really common for NFT standards to allow for machine readable metadata that contains things like traits and rarity. If we allow multiple inscriptions on the same sat, you can put the inscription proper in the first inscription, and then put the traits and other metadata in a second inscription with the title metadata with type application/json. Block explorers can then look for this additional inscription and use its contents as metadata.

We could also consider using a different field for #943. As an alternative, we could have a "name" field, and have it be different than a "title". Title might be for human readable titles, and "name" could be more like a filename. This would also allow giving inscriptions nice filenames when downloaded.