Annotation navigator: replace locked user table with text

Using a whole table for potentially one entry was too much.
Annotation navigator: make neuron node skeleton table slimmer
Annotation navigator: add 'last used' column to annotation table
Annotation navigator: sort annotation table by name by default
Annotation navigator: add usage number column to annotation table
Annotation navigator: add name regex search to annotation table
Annotations: make sure queried annotations are distinct
Annotations: improve query performance for last used and usage fields

This commit changes the extra last used and usage count fields of an annotation
query to explicit SQL. This improves the query performance considerably. That is
because the Django syntax used before referred to the joined tables which are
much larger than the single tables actually only required which are used now.
Annotation search: add better styling for result table
Annotation search: link checkboxes of entries for same entity

Due to the expansion of annotations it can happen that an entity (like a
neuron) is in the result list multiple times. This commit makes sure that when
clicked on a checkbox of such an entity, the checkbox of its clones will also be
toggled.