discovery plugin cleanup

Because of JBDS-2361 and JBIDE-12556 I spent some time reviewing the discovery plugin.xml and found a few items.

I'll put my raw list in the comments, but here are the highlights:

• new connector ID's should not use the same name as the feature they refer to; this is so project examples can refer to them as "the maven plugins" instead of "org.eclipse.m2e" when it might be a different name.

• The word "Free" is added to some entries but not to others.

• egit and egit.mylyn are two seperate things (good), subversion/subclipse.mylyn is one big one (bad). [incorrect - there are actually two for svn too]

• eclipsecs includes experiemental com.github.sevntucheckstyle feature - do we need/want that [yes for now]

• common.mylyn.feature - can that be split into bugzilla and jira one ? [no - bugzilla/jira setup currently are connected]

• jrebel requires server_core feature but why aren't they just listed in there and remove the need for seperate core/server feature ? [cant be done without license problem]

• Maven connectors seem to be too fine-grained, why do we have m2e,m2e-jdt and m2e-wtp as separate connectors ? [can wait]