SVG overlay: make active treenode's Z also a project space coordinate

This way all three X, Y and Z are project space components. In its current
implementation this only works for XY views.
Statistics widget: add more information to cell data
Return User IDs instead of user names on user history query
Selection table: support opening a pre-created instance

This allows to preconfigure a selection table from other places and give
it to the window maker to open it.
Add API to query skeleton IDs based on different constraints

Currently the result set can be constrained by a certain user that has
to be creator of at least one treenode, a certain user that has to be
reviewer of one of the skeleton's nodes and an additional time frame
that can be set for both events.
Statistics: create pre-populated selection table for node statistics

The number of nodes a user has created or reviewed in a certain time frame can
now be clicked (if non-zero). A new selection table is created and pre-populated
with the skeletons the respective nodes are part of.
Fix small inconsistency in neuron name service

This wasn't a problem so far, because this method isn't used.
Merge branch 'node-lists-from-statistics'