Filtering interface based on Duplicator

See #2245
Add filter controls

#2245
Whitespace
Add suggestions
Introduce different search types
Display unique suggestions
No duplicate queries
Unify dropdrowns and filter actions
Initial steps to implement calendar in filter suggestions
Make filters responsive
Delay suggestion menu
Save filter drawer state per section

See #2245
Fix calendar styling and behaviour

See #2245
Documentation, clean-up, bug fixing (filters, calendar, suggestions)
Make calendar default to midnight

Only applies if no default date is set.
Include @brendo's issue-2003 branch
System date filters

Fixes #2003
Implement token suggestions
Restore DS editor suggestions
Don't hardcode 'is' filter, provide it from the field with no predicate. RE: #2245