JIRA 198: nested annotations. Better support for nesting graphs. Added a new field Ontograph.nesting_level which determines the possible nesting among graphs (e.g. 3 can be nested inside 1 or 2). The default is 0, a special number that prevent any nesting. The annotation tool will automatically determine and save the nesting among graphs and is able to cope well with multiple containing graphs. Also improved the way the annotator display status messages and handle AJAX response errors.