CORE-4601, CORE-4643, CORE-1848:
* Ensured that only the lists of simple selection argument types are
parsed for default values. Tree selections used to be included in this
check, which is not the intent.
* Simple list deletion issue has been corrected.
* Fixed issue where app editor comboboxes were not initially showing
their default text ("Choose").
* Corrected combobox relaunch issue where previous value did not appear
to be set on re-launch.