Summary:
Flaky Dates test failures related to the use of JQuery autocomplete for time
zones, which wasn't working well.
This diff replaces that autocomplete (as well as a similar select box in
DocumentSettings) with our newer autocomplete, adding some select-box like
behavior.
Most of the behavior is factored out into ACSelect, which could be more
generally useful.
Adds an option to autocomplete to keep options ordered according to their
initial order.
Unrelated: fix up usage of MultiHolder in Drafts to avoid 'already disposed'
warnings.
Test Plan: Fixed several affected tests.
Reviewers: jarek
Reviewed By: jarek
Differential Revision: https://phab.getgrist.com/D2919
