Summary:
Follow up of D32665064, this diff moves all plugin management logic from flipper-ui to flipper-server. Things like downloading, installing, querying new plugins.
Loading plugins is handled separately in the next diff.
Reviewed By: nikoant
Differential Revision: D32666537
fbshipit-source-id: 9786b82987f00180bb26200e38735b334dc4d5c3