This commit adds radicle-explorer, a web interface for Radicle which displays
repositories, issues and patches.
The package builds the web interface itself, but a web server still needs to be
configured to serve it. This is out-of-scope for this commit, but may be added
to the related NixOS modules in the future.
The web interface is based on the API exposed by radicle-httpd. For this reason
the sources and version of the web interface have been tied directly to the
radicle-httpd package, necessitating corresponding updates on this package
whenever httpd is updated.
There's a little bit of fixed-point magic in this change to enable two features:
* Overriding build-time configuration (required to, for example, display a
different Radicle seed by default). Documentation for this is available in the
upstream repo.
* Building radicle-explorer without plausible, a web tracking package which
sends user-data to a remote host by default.
These are configured through slightly different overriding mechanisms, but I
hope to simplify this in the future with some upstream patches.
