Regression in [0] which displays the filename for the active
theme but still used the label internally.
This meant actions such as removing the theme would not always apply
to the name being displayed.
- Adding a new theme was not setting it active.
- Detecting if a theme was built-in used the run-time label as a lookup.
- Theme removal first require it to be re-selected.
[0]: 0bb6317035
9e09351b5b