Dataviews: Add real hyperlinks

This adds a real hyperlink in all the <a> tags in the dataviews. That way,
one can open a Stack in a new tab, or bookmark the link.
Dataviews: only execute JS link

Added "return false" to all JS links to prevent default browser behaviour
(following the link). That way the address bar is not changed when simply
clicking a link.
Neuron Dendrogram: add tool infrastructure and skeleton loading

The neuron dendrogram will eventually display a neuron as a tree structure (i.e.
a dendrogram). This commit adds basic tool infrastructure to create its window
and to open it by pressing F4 while in the tracing tool. A button will follow.

Also, the functionality to retrieve the nodes of a skeleton is added and to
transform it into a tree structure that is known to D3.
Neuron Dendrogram: display basic dendogram for current neuron
Neuron Dendrogram: select treenode on dendogram node double click
Neuron Dendrogram: color all links downstream from a tagged node

The tag to test against can be specified by the user.
Neuron Dendrogram: collapse nodes that are no branches and are not tagged
Neuron Dendrogram: make tree collapse optionally

A checkbox is added to make the collapse of non-branch and non-tag nodes
optional.
Neuron dendrogram: color tagged nodes
Merge branch 'neuron-dendrogram'
Neuron Dendrogram: fix node selection

Due to some refactoring before a bug sneaked in that prevented a user from
selecting a treenode by double clicking a dendrogram node. This is fixed now.
Neuron Dendrogram: add option to disable the display of node IDs
Ensure indexes on creation_time and edition_time of location based tables

When the location based tables were re-designed lately, we forgot to add indexes
on creation_time and edition_time. This commit fixes this by creating them if
they are not already there.
Fix existence test of index creation migration
'F' adds tag 'microtubules end'

This tag is used from e.g. AnalyzeArbor or a tag-based coloring mode in 3D Viewer.
Upgrade d3 library to v3.4.11

I tested it with all the widgets and it seems to work without any problems. The
reason for updating is its use in the neuron dendrogram. Some options have been
added in v3 that allow better control over node placement.
Neuron dendrogram: make container element have correct hight
AnalyzeArbor: pie charts for fraction of inputs and outputs on each region.
AnalyzeArbor: generalized function to create pie charts into SVGUtils
SkeletonConnectivity: generalized multiple bar chart function into SVGUtils

Also fixed the incorrect axis name (used to have the widgetID and it shouldn't).