Pre-load local cache

[micksmothers]

Feature request:

As a Plex-aaos user I would like to allocate a fixed amount of local storage to pre-cache songs from the currently playing playlist so that the playback experience is less susceptible to interruption due to network issues.

Suggestions: maybe a sliding scale from 100MB to 2GB or such?

Acceptance criteria:
Scenario: shuffle enabled
When the user has enabled the shuffle option
Then the cache should be in the order of the shuffled track list

Scenario: playlist change
When the user has selected a new playlist
and has initiated playback
and the first song in the playlist actually starts playing
Then the cache should be replaced with a new cache from the newly selected playlist

When the user has selected a new playlist
and has not initiated playlist
and switches back to the originally playing playlist
Then the cache should be maintained

[joeyberkovitz]

Seems like a dup of #3 with some additional details and features. I'll merge them later