Allow template strings as parameters to modify calls.

This allows for, among other things, modification and formatting of existing fields. I.e. album='$album [$label]'
Value must be single quoted to avoid the shell picking up $'s.
Use id instead of mbid when looking up missing tracks, to account for data provided in a plugin. Also, when showing missing tracks, show ALL tracks on album, with existing tracks marked with + and missing marked with -.