Minor fixes and Tree update

- Contains a couple of minor fixes to arethusaUtil as well as search.
- Works on the display of subtrees in dependencyTree.

A subtreeFinder service is added which is currently unused. It could be used to draw several independent tree-graphs, which independent zoom and pan behaviour.

The service is relatively straight forward and returns an object, where the keys are root nodes of subtrees and the values are arrays of node ids (including the root node itself).

Practically this is not that trivial, especially the placing of the inital subtrees. We'll leave that for future work.

At the moment subtrees are drawn `inside the same graph (`<g>`) element`. If a treebank template has NO head specified (as in: empty string), nodes will only be placed in the graph once they have a valid head. This takes out the initial display of a tree where all nodes hang on root.

You can gradually build your tree, subtrees will be added to the graph, even if somewhat static right now, as each subtree is just placed next to other subtrees (the root node is a subtree of its own)

Needs more thought.