Create a dgrants-js library

[apbendi]

Currently, all protocol interactions are simply implemented in the frontend. In the long run, we'll want to provide better developer tools, such as a library that abstracts over protocol interactions and implements protocol standards. Other developers could use dgrants-js to build their own clients, backends, etc....

This tasks is simply to set up the dgrants-js library as another sub-project in this monorepo. It should be imported and configured by the app, and any simple low-hanging fruit can be extracted from the frontend and implemented internally instead.

Moving forward:

• New protocol functionality, like the metaPtr resolution and fetching described in Change MetaPtrs to Include Discreet Storage Type #481, can be implemented in this library
• Existing protocol functionality can be further extracted from the frontend and moved into this package