%near app frontend: gateway browser

[hanfel-dovned]

The frontend portion of #17. Users should see a list of their installed frontends and a list of frontends they've heard about. You can open installed frontends and install heard-about frontends. You can also manually install frontends using metadata with the poke that will be specified in #17.

This should follow the UF's frontend design patterns.

[hanfel-dovned]

This should also have a UI element for creating a new gateway. See #20.