Bump to pom-imagej 2.7

This also updates the code to account for API changes in
imagej-common 0.5.0.

Lastly, it temporarily pins to imagej-updater version 0.2.0,
since pom-imagej 2.7 failed to preemptively bump that version,
and temporarily pins imagej-launcher to 2.0.3, since the
version 3.0.0 set in the parent has not yet been released.
POM: add profile to generate aggregated javadoc

Thanks to Johannes Schindelin for blazing the trail there with Fiji:
https://github.com/fiji/fiji/commit/25d5510917a2d091d998f2489dc91edb3e6ec0c8