Fix for translating dynamic enumeration values containing periods.

Since these are effectively user-supplied, we need to make sure we don't
blow up when users (rightly!) add punctuation characters.
Fix click on combobox scrollbar causing list to close
Introduce advanced search to the staff interface.

Adds support for searching on different field types (text, boolean, date, enumeration).

Changes the way advanced search fields are defined in the staff and
public interface.  A new "AdvancedSearch.define_field" provides a
declarative way of indicating which fields are searchable, their types,
and how they map to the underlying Solr fields.
Allow field queries to be marked as 'literal', meaning they'll be escaped from Solr query syntax.
Updated the plugin README to cover the new advanced search and a small tweak to branding.
Update date operator labels
Clarify the related agents code by naming the date handling method.
Generalise related agents code to let us model relationships that have directions.
Change the way we store relationship directions so it works for non-global records too.

Previous we would store 'relationship_target', which was the URI of the
record that a relationship pointed to.  This worked fine for global
records, but could be troublesome for repository-level records, as these
can have different URIs over their lifetime if transferred between
repositories.

Now we store a pair instead: the record type and its ID.  This should be
stable throughout a record's lifetime.
Change the new directional relationship API to be a drop-in replacement for define_relationship
Add backend implementation of hasPart/isPartOf
Add support for the bound_with relationship too
Switch both relationship types to use the same JSON property
Remove staff_field_query_field schema and enumeration references as they are no longer used.
Frontend changes to support the new types of accession interrelationships.
Make 'true' the default value for the advanced search boolean query
Make sure related accessions don't interfere with spawning resources.
Code review suggestion: use the display string when showing related accessions in the read-only view.
Added missing I18N values for new accession relator types
Fix the 'Related accessions' anchor in read-only view