Reworking the NeuroML export.
Needed to export in micrometers rather than nanometers,
and to export a list of skeletons each as a NeuroML Cell.
Synapses are still not defined, and there is no entry in urls.py
or access from the web client yet.
Merge branch 'master' into neuroml
More fixes for NeuroML export. Exports the XML but correctness has not been validated yet.
Fixes for exportneuroml.py

The Segment vs SegmentParent objects in NeuroML python are not entirely clear to me.
Merge branch 'master' into neuroml
Merge branch 'master' into neuroml
Export for NeuroML Level 3, version 1.8.1 (validated).
Classifications: add support for root retrieval of project lists
Add admin tool "Tag Based Classification Graph Linker"

The tool introduced by this commit adds a new custom admin view with
which one can link classification graphs to projects in an automated
fasion. This is done based on the attached tags of a project. The tool
finds tag sets and offers to unify the linked classification graphs
or projects within those tag sets.
Add optional importer step to link suggested classifications

This commit introduces a new optional option called "Check
classification links". When checked a new importer step is added after
the project selection. This step suggests existing classification graphs
to be linked with the new project(s). The suggested graphs are project
independent and have the the same tag set (or a super set of it) as the
new project(s). The user is then free to mark those classification
graphs for automatic linking after the final confirmation step.
Fix small typo in documentation
Merge branch 'classification-admin-tools'
Fix wrongly named view "skeleton_neuroml" in URL configuration

The correct name seems to be "skeletons_neuroml".
Fix 'r' key to properly find an open node when the active node is tagged,
or when a node had tags additionally to tags that mean "end".
tree_util: avoid creating a new list for no reason.
Remove print statement.
Handle potential errors when invoking createPresynapticTreenode.
NeuroML Level3 1.8.1 exporter may be a bit less bad. Loads into neuroConstruct.
skeletonexport: sanitize argument for SQL command.
export_NeuroML_Level3: fix error whereby many segments were skipped.