Venn Diagram: properly select only the subset of models that are not common
when clicking on a single circle.
Merge branch 'master' of github.com:acardona/CATMAID
Venn diagram: handle clicks properly in the case of false overlaps
because of improper layouts.

Also make the text label of each circle respond to click.
3D viewer: change setClearColorHex() to setClearColor()

The former function is deprecated and Three.js warns about this in the
console.  setClearColor() can be used just like the setClearColorHex()
function.
Connectivity widget: fix check-box behavior

As reported in issue #688, the selection check-boxes didn't keep their
state when the threshold was changed. This commit fixes this by
maintaining the selection state of each skeleton (and check-box) in as
member field of the widget itself. Thus, when refreshed, the state isn't
lost and can be reused. This fixes #688.
Fix general focus catching of UI (e.g. un-focusing inputs)

The UI object has a catchFocus() method to un-focus the currently active
element (e.g. a text input field). This is done by focusing an empty
anchor element (the 'focusCatcher'). This element doesn't accept any
input and so all keyboard and mouse events can bubble up. Calling
focus() on this element does, however, only work if it is a proper
anchor, i.e. if it has a 'href' attribute. This commit adds this
'href' attribute and (un-)focusing now works properly.

Thanks to Nils Holger Kranenburg for reporting this issue. The original
problem leading to this was the following: When jumping to a specific
slice by entering its slice number into the z-index input box of the
Navigator/Move tool followed by pressing Enter, the focus would remain
in this box. So even after one clicked into the image to e.g.  pan, one
couldn't use the plus and minus keys to change the scale. After this
commit, the input box is un-focused after clicking the mouse on the
image.
Navigator: Show position marker in all Stacks

Shows a "Position Marker" (duplicate mouse cursor) in all open Stacks.

The code has been is copied from the Selector tool.
Navigator: Change position marker to a simple cross
Navigator: Move position marker while dragging
Navigator: Move stack only on left mouse button drag

Let the Navigator only catch the mousedown event if it comes from
a left mouse button. Before, a right click would open a context
menu but also trigger the move action.
Tracing Tool: inherit basic actions from navigator
Tracing Tool: change existing actions to use prototype
Navigator: Remove redundant definition of 'onmousewheel'
Navigator: Don't modify statusbar
Navigator: add addAction function
add static data dir to urls
Navigator: some cleanup

- renamed onmousemove.move to onmousemove.drag
- whitespace
Navigator: Hide position markers onmouseout

Hide all position markers when the mouse leaves the focused stack.
Otherwise they would remain somewhere near the edge.
Navigator: Make strict
Remove Selector tool

The "Position marker" functionality (duplicate cursors in all open Stacks)
is now in Navigator. Other than that, the Selector didn't add any features
and wasn't used anywhere.