Summary:
Sorry for so long diff, but actually there are no functional changes, just refactoring to make further changes of Plugin Manager easier to understand.
I've de-coupled the code related to plugin management from UI code and moved it from PluginInstaller UI component (which will be replaced soon by new UI) to "flipper-plugin-lib". So pretty much everything related to plugin discovery and installation now consolidated in this package.
Additionally, this refactoring enables re-using of plugin management code in "flipper-pkg", e.g. to create CLI command for plugin installation from NPM, e.g.: `flipper-pkg install flipper-plugin-reactotron`.
Reviewed By: passy
Differential Revision: D23679346
fbshipit-source-id: 82e7b9de9afa08c508c1b228c2038b4ba423571c