Add option to speed-up remote review with checkbox.

Default is false, which is the old behavior using E to go to the next
segment. If enabled (true), after 2 times pressing W it automatically
jumps to the next unreviewed segment, sets the actual segment's review
status to 100.00 on the client side and does not refresh the widget,
thus speeding up reviewing of the long tail of very short segments.
user-evaluations: server-side python code, first draft.
User evaluations: added analysis of missed synapses.

Unfortunately removed synapses are not logged, so these cannot be detected.
Fixed up user analytics for django admin page.

Still could use some more work, but at least now:
 * users are sorted by last name
 * start and end dates are choosable
 * removed one plot that was not so useful (lower left)
 * extended lower right plot (usage bouts) to fill up the vertical space
user evaluation: count synapses added by other users
after the creation of a treenode by the user under evaluation.
Pre-seed user analytics with current date and 10 days back.
Correct typo in docs.
Created new admin page for tracking user proficiency over time.
user evaluation: add plot of missed pre, post and nodes by percent.
Circuit Graph Plot: added export to SVG and CSV.

Results in files being downloaded, directly from javascript thanks to FileSaver.js.

Notice that the CSS stylesheet had to be hard-coded into the plot,
otherwise the downloaded SVG lacks a few style attributes.
Fix up export widget to properly download files
(rather than open a new window).
Export to SWC: properly download a file
rather than open a new window with the SWC text content in it.
Merge branch 'user-evaluations'
Graph: nodes must be visible to be considered as selected.

The issue stems from cytoscapejs UI selecting hidden nodes when
selecting multiple nodes with a mouse-drawn rectangle.
Added comment to user_evaluation.py
Continue loading also when there was an error
Selection Table: toggle select all now works only for those matching a search string if any.
Merge remote-tracking branch 'origin/master'
Selection Table: checkboxes to toggle all pre or post.
Selection Table: add buttons to sort by name and by color.