JBIDE-16574 : make m2eclipse-egit an optional required import O_o

Using p2.inf black magic to make m2eclipse-egit required import optional in org.jboss.tools.maven.feature.

Also made all other jboss maven features depend on org.jboss.tools.maven.feature, so that m2eclipse-egit is installed whenever one of these is installed.

Signed-off-by: Fred Bricon <fbricon@gmail.com>