Componenttree refactor

Refactoring of the net.imglib2.componenttree package.

In a nutshell: sanitize interface/class naming and introduce interfaces to represent the actual component tree/forest.

In more detail:
* renamed ```ComponentTree``` to ```BuildComponentTree``` to make clear that this is
  the algorithm to build component trees, not the tree itself.
* renamed the old ```Component``` interface to ```PartialComponent``` because it represent
  an incomplete component on the component stack. The classes implementing
  it have been renamed from ```...ComponentIntermediate``` to ```...PartialComponent```.
* introduced a new ```Component``` interface representing completed components.
  This contains basic methods to get the pixels of the connected component
  and navigate the component tree.
* introduced new ```ComponentTree``` and ```ComponentForest``` interfaces that just
  provide the ```Component``` root(s) of a component tree.
* ```PixelListComponentTree``` and ```MserTree``` implement the ```ComponentTree/Forest```
  interfaces. ```PixelListComponent``` and ```Mser``` both implement ```Component```. This
  allows to use the same code to visualise both pixellist and mser trees,
  for example.

Comments?