Update release instructions for ImgLib2
Tell Maven that pom-scijava is not local
Remove obsolete ImageJX list from mailing lists
Remove superfluous .git suffixes
Move the ImageJ launcher to its own repository

The new repository is:
https://github.com/imagej/imagej-launcher

The launcher's development cycle differs from that of ImageJ2 core, and
the launcher is also used by ImageJ1 and Fiji. It makes sense to version
it separately and hence have it reside in its own Git repository. Doing
this also makes the ImageJ2 build much less complex.