Update plugins documentation

[taras-z]

Summary

It would be nice to read updated information about provided official and community plugins that can lower the entrance level to new users and developers.

The Plugins page contains:

1. descriptions not for [all plugins],(https://github.com/nasa/openmct/blob/master/src/plugins/plugins.js)
2. broken links.

Solutions

There are a few ways to improve plugins documentation:

1. Update the page manually:
   1.1. by hand (for example, monthly),
   1.2. check changes by git history and update descriptions.
2. Update the page automatically:
   2.1. by scheduled routine (for example, weekly),
   2.1. generate (compile) the page from a partial description of each plugin (for example, from README.rd in a plugin folder).