mrconfig: move legacy-imglib1 back to fiji

As discussed here:
https://groups.google.com/d/topic/fiji-devel/KObyQZ0R_1Q/discussion

The consensus seems to be to keep ImgLib1, and downstream
projects like TrakEM2, in core Fiji, at least for now.
Add configuration for BigDataViewer GitHub org

As discussed here:
http://code.imagej.net/chatlogs/imagejdev?times=prefix&start-date=2014-11-18&start-time=0400&end-date=2014-11-18&end-time=1200