Bugfix: strip commas from group header HTML id attributes.
Comma is an illegal character here, and its presence will cause attempt
to append views via this selector to silently fail.
Fixing, updating som type annotations.
GroupedCollectionView cleanup.
Removing extraneous params, fixing/adding some type annotations.
Moving logic to remove group from applied groups into #clear_grouping.
Fixing GroupedCollectionView#reset to work with multiple groups.
Changing GroupedCollectionView#find_by_keys to find_or_create_by_keys
Remove empty groups and group header DOM elements.