Ontology search: add basic widget infrastructure
Classification search: add search steps infrastructure
Classification search: add feature selection tree

This commit adds support for the display and selection of ontology features to
the classification search. All children of "classification root" are displayed
as a tree, including relations. All of them are selectable.
Ontology: move feature path creation in ontology namespace

The methods and classes related to this were part of the clustering
namespace, because this was the only place where they were in use. This,
however, will change and also semantically they belong into the ontology
namespace.
Ontology: make feature read-out more robust
Classification search: display 'unfolded' ontology features

Due to relations like "is_a" the ontology display used so far (the one of the
ontology widget) is compressed. For every "is_a" relation there is a separate
path. This commit changes the current display to show all possible paths. Right
now only as a list, bit this will probably change in the future to a tree.
Ontology/classifications: re-organize feature generation

This commit moves all the feature and graph search functions to the
classification namespace. They fit much better there.
Classification search: add basic search widget
Ontology search: add possibility to define default filter tags
Ontology search: combine features of different ontologies with OR

Selected features of different ontologies are now combined with OR while
all features within one ontologies are combined with AND.
Merge branch 'ontology-search'

All conflicts have been resolved to include all changes of both parents.

Conflicts:
	django/applications/catmaid/control/classification.py
	django/applications/catmaid/static/widgets/themes/kde/screen.css
	django/applications/catmaid/urls.py