First try of reimplementing the gridtree visualizer as vaadin component. Still
missing:
	- colored matchings
	- mark the base level when hovering nodes
	- tooltip should display the namespace of the node, not the depth of the
	  tree
	- island feature which, should be solved generic in AnnotationGrid.
Mark matching nodes in grid tree
The tok row is labeled as tok. This reformats the tok row automagically.
Highlighting base row by hovering the nodes works in gridtree again.
Indexshift is made by AnnotationGrid not by GridTreeVisualization.
Add tooltip to gridevent for having more controll about the tooltips. Gridtree
could not use the row caption for tooltips, but the namespace + annotation key
for every GridEvent.
Restrict the graph traversal to nodes with annoations of the triggering
namespace.
Make the Annotation token line configurable. There is now an additional
constructor for defining the token row, which is used. If no explicit token row
index is set "tok" is assumed.
Remove the old, iframe based gridtree visualizer.
Reimplementation of the gridtree visualizer. It is now based on vaadin
components and supports spans as token row.

fixes #168

Merge branch 'rewrite-gridtree' into develop