[mythtv-theming] New music metadata fields

[Richard Hulme]

Hi,

Commit 0fb11bd - https://github.com/MythTV/mythtv/commit/0fb11bd - adds 
support for reading the disc number and disc count fields from mp3 
files.  These fields are added to the metadata map, so pretty much any 
screen that shows the track number can now also the disc number and disc 
count as required with the 'discnum' and 'disccount' fields respectively.

Commit a9e8f44 - https://github.com/MythTV/mythtv/commit/a9e8f44 - adds 
'discnumspin' to the editmetadata window.

You may wish to update your themes accordingly.

Richard.