Added and removed documentation to/from overlay_node.
Started refactoring SkeletonAnnotations -- work in progress.
Fix whitespace in init.js' updateProjects methods
Data views: only close current project when loaded from menu

Up to now the loading of a data view (the front page) caused any open
project to close. This commit changes this behavior to only close the
current project (and its windows) when the user opens a data view
through the data view menu (appearing when hovering the "Home" link).

Projects loaded with the help of a "URL to this view" link, now won't
get closed immediately anymore because of loading of the default data
view. This is related to isuse #537.
Make sure initial stacks get first loaded after login completion

The URL to a CATMAID instance can contain information about which stacks
to load at startup. Such a URL can be created with the help of tho "URL
to this view" link. The loading of these stacks, however, requires the
login procedure to have finished. This commit makes sure this is the
case by loading initial stacks in a callback method passed to the login
command. Without this, the handle_updateProjects() method would destroy
the newly created project right away. The callback is instead executed
*after* the potential deletion of an existing project. This is related
to issue #537.
Merge remote-tracking branch 'origin/master' into svg-overlay
Add region of interest models
Add ROI creation and retriaval views
Classification editor: add option to add ROIs to context menu
Classification editor: remove jsTree UI plugin to make ROI links work

The UI plugin of jsTree adds hovering and selction functionality to
nodes. However, it doesn't allow any click event to pass through to the
actual node. This in turn is needed to make links in a node, e.g. to a
ROI, work. Therefore, the UI plugin has been removed for now.
Classification editor: add completion callback to tree loading
Classification editor: display ROI links if available
Classification editor: allow user to close a displayed ROI
ROIs and classification editor: allow removal of ROIs
Classification editor: add temporary cancel button to Roi tool
ROIs: allow to retrieve (and auto-create) cropped ROI images
Classification editor: display ROIs when hovering ROI icon
Classification editor: make ROI preview optional
ROIs: allow auto creation of cropped images on ROI creation

By default this is switched off, but it can be activated by setting
the ROI_AUTO_CREATE_IMAGE variable to True in the settings. If
activated, an asynchronous Celery task is launched after the creation of
the ROI.
ROIs: delete cropped image files (if any) when ROI is deleted