Create new pixel fusion to implement simple overlap.

In fact, this is not a real fusion but a simple overlap of one image over the others.
Add "overlap" option in fusion methods.
Rename the "overlap" option with something more descriptive as suggested by Dr. Preibisch.
changed name of Ignacio's fusion method again to "Intensity of random input tile"
increased stitching-internal version
Merge pull request #17 from fiji/no-fusion

No fusion - Adding a new fusion method that randomly takes the input pixels of one of the overlapping views at each pixel where many views are overlapping (actually it takes the last one in the list of overlapping views)