D25999: Add optional subtitle to grid delegate

[Nathaniel Graham]

ngraham edited the test plan for this revision.

REPOSITORY
  R296 KDeclarative

REVISION DETAIL
  https://phabricator.kde.org/D25999

To: ngraham, #vdg, #plasma, davidedmundson
Cc: kde-frameworks-devel, LeGast00n, GB_2, michaelh, ngraham, bruns