The rule editor's value box built its suggestions from libraryStore's
whole-library arrays, which made it one more reason to load every
track at startup, and left it empty when they had not loaded.
SuggestSmartPlaylistValues answers with up to 50 distinct values of a
field that contain the typed text, from the same joined row the rules
match against, so a suggestion is always something a rule can match.
yj-combobox announces its filter text so the editor can ask, debounced
and cached per field and text.
Refs #279
yonlu
3cddf70c4d