Change the results of `getPlugins` to not wrap the results of `getPlugin`

[balupton]

Currently getPlugins returns something like {version, description, homepage, compatibility} for each plugin - where compatibility is the result of getPlugin - I'm not not sure this makes sense, and that instead it should forgo {version, description, homepage} and just return the results of getPlugin for each thing. If more data is needed, then that should be added onto getPlugin instead - and extra data can be request via opts