Column Browser Design

The purpose of the column browser is to provide a way to filter down the list of songs in the library. This has a couple of big use cases:

1. Finding a specific song. The column can be used to find a specific song by narrowing down the view to displaying a smaller set of songs. This is helpful if you can't remember a songs name but you know other attributes of the song such as (primarily) what album it's on, the genre, and (secondarily) if it's track 5 or has 4 stars.

2. Filtering the list of currently playing songs. The column can be used to create sort of "temporary playlists" by filtering the list of currently playing songs. This is useful if you'd like to listen to a specific genre, artist or album. This mental model implies that non-traditional columns such as "composer" "Producer" "record label" or "star rating" could be useful.

Behavior:

* Positioning.
    * Browser positioning should default to "Automatic" based on screen size, with the option to force "Left" and "Top" [DONE]

* Column Headers:
    * Columns should have headers that display what the column contains, such as "Artists" [DONE]
    * Primary click on column headers scrolls to the top and selects the "All" filter [DONE]
    * Alternate click on column headers should allow for hiding and showing of available columns as well as setting the positioning of the browser. [DONE]
        * We should make sure that as long as the browser is enabled one column is always shown. The last item should be made insensitive to disallow a situation where we're unable to get the browser back. [DONE]

* Filtering:
    * All Columns should be prefixed with a filter "All # %NAME" where %NAME is the name of the column such as "Artists" or "Genres" and # is the number of available items in the browser such as "All 30 Genres" [DONE]
    * Columns should filter other columns "below" them, but not "above". For example, selecting an Artist should filter down the selection of Albums, but not genres. [DONE]
        * If a higher level column is selected that doesn't apply to a lower level column (for example, select the genre Jazz for the band Weezer) the lower level columns should be reset to "All" to avoid an impossible selection. [DONE]
    * If you've selected (for example) an artist in the browser, the artist column should be hidden in the media list. [TODO]