ui: Also match group names when filtering tracks

- If a group is matched:
  - The group appears in the list as-is and is manually collapsible as
    normal.
  - When expanded, all the tracks are displayed inside (that is, they're
    not filtered).
- If a group is not matched:
  - The tracks inside are filtered.
  - If any tracks match then the group is rendered auto-expanded and is
    no longer manually collapsible.
  - If no tracks inside the group match the filter, the group is not
    rendered at all.

Change-Id: I645b54e3cea397df58defdf3d42009d466a7c01b