Adding FriBID browser plugin

FriBID is an open source software for the Swedish e-id system called
BankID. FriBID also supports processor architectures and Linux/BSD
distributions that the official software doesn't support.

https://fribid.se/index.en.html

FriBID plugin is a firefoxWrapper plugin. Enabled by setting:

  nixpkgs.config.enableFriBIDPlugin = true