* [explore] fix autocomplete on verbose names
Currently when searching for metrics or groupbys, the autocomplete
search functionality only matches based on the metric_name, though in
some cases the verbose_name is displayed and disregarded for search
purposes.
Also another issue is that not all pre-defined metrics show up in the
drop down which is confusing. Users may have simple metrics for which
they setup a nice verbose name and/or description and expect to see
those in the dropdown.
This PR addresses it for metric and column-related dropdowns.
* Add unit test
