Support queuing folders without entering them

[Will Lunniss]

This will be quite a big one.

A the moment you can only queue tracks in the current folder, you cannot queue tracks in sub folders. This means you cannot queue an album from the artist view, and cannot queue up all the albums in an artist at once. Same applies for other views such as the folder view.

Solution is to traverse the child directories and load their content as needed. However, some protection will be needed though to prevent queuing the entire music library as it could take a very long time to fetch the entire directory structure.

[Will Lunniss]

This is paritally implemented in 2.0

[Casey McGinty]

+1 for queuing all the albums from a single artist in the artist view.