Use "<missing values>" in the sidedef tabs, and show it in gray.
Merge pull request #116 from eevee/fix-propgrid-multi-values

Use "<missing values>" in the sidedef tabs, and show it in gray.
Fix serious oversight in entry sorting code. Oops.
Merge pull request #117 from Gaerzi/master

Fix serious oversight in entry sorting code. Oops.
Merge branch 'master' of https://github.com/sirjuddington/SLADE into Music