[FR] Notify when a plugin gets released out of beta, and add command to remove non-beta plugins

[FeralFlora]

After plugins are released out of beta to the Community plugin store, it is redundant for BRAT to be keeping them up to date. If you have many beta plugins installed, the process of manually checking which plugins can be removed from BRAT is a bit tedious. Therefore, it would be nice if BRAT could notify when a plugin gets released out of beta, and preferably also have an option to remove all non-beta plugins from BRAT.