Object Tree: "Cleanup fragments" popup menu entry
which prompts for a minimal size in skeleton treenodes
for skeletons to be sent to a neuron under the 'Fragments' folder.
The new neuron is named "Fragments" plus the date.
If the small skeleton exists in a neuron that only has one skeleton,
that whole neuron is sent 'Fragments' group.
graph2: fix error when splitting both by confidence and by synapse clustering
when there is a single neuron to expand by synapse clustering
and none other to split by confidence.
Graph widget: more robust way of detecting what kind of data the server sent.
node.py: remove one unnecessary table join
node.py: minor optimizations
node.py: avoid declaring SQL variables that are then not used.
node.py: sanitize project_id and avoid creating an implicit cursor
graph2.py: better parsing of treenode.location
graph2.py: more robust dual split by both confidence and synapse domain.

Before, could fail in error when a small chunk of the arbor lacked synapses.
node.py: fix error in querying tags

Thanks to Matt Berck for reporting.
webglapp: synapse coloring mode
Two modes:
 1. pre/red and post/cyan, like until now
 2. heat-map coloring, by number of synapses with/from a partner neuron
webglapp.js: make synapse coloring robust to not having one or the other
type of synapses.
Local client-side caching on request in review widget

Conflicts:

	django/applications/catmaid/static/widgets/review.js
	django/projects/mysite/urls.py
Cache image tiles segment wise.

Start google chrome with increased cache size (2GB) using

	--disk-cache-size=2000000000
Fix a bug in the review widget and speed up jumping to low node-count
fragments

The issue arose when calling initReviewSegment with an index
that was based off an array extracted with .slice() which does
not match the skeleton_segments index.
Add review puffer when reaching end of segment to review
Slice caching in pure javascript
Remove unused cache_image Python code
Remove caching from urls.py
Upper limit on the number of nodes to cache