Add log4j SLF4J binding to fiji-compat

Dscho and I discussed, and decided that the best place to put "blanket"
dependencies for Fiji is in fiji-compat. We were already doing this e.g.
for ImageJ2 (ij-app), so it makes sense to include others there as well.
These dependencies are artifacts intended to ship with Fiji, but upon
which no specific Fiji plugin from src-plugins depends directly. By
including them as runtime dependencies of fiji-compat, we ensure that
building Fiji from source will still include these artifacts in jars/.
fiji-compat: tweak ImageJ2 dependencies

The fiji-compat component does depend on ij-core, but not directly on
ij-app. However, we *do* want ij-app (and all its dependencies) to be
part of Fiji, so we still include ij-app as a runtime dependency to
ensure it is still included.