NEXUS-4766 - Added "classifierSeparatorChar" config attribute to archiver mojo to avoid problems with nexus snapshots.
Nexus could not handle snapshot artifacts having . in their classifiers. This is a workaround for that.

Conflicts:
	tycho-p2/tycho-p2-director-plugin/src/main/java/org/eclipse/tycho/plugins/p2/director/ProductArchiverMojo.java
	tycho-p2/tycho-p2-director-plugin/src/test/java/org/eclipse/tycho/plugins/p2/director/ProductArchiverMojoTest.java

Conflicts:
	tycho-p2/tycho-p2-director-plugin/src/main/java/org/eclipse/tycho/plugins/p2/director/ProductArchiverMojo.java

Conflicts:
	tycho-p2/tycho-p2-director-plugin/src/main/java/org/eclipse/tycho/plugins/p2/director/ProductArchiverMojo.java
Performance improvement: caching installableunits converted from maven artifacts to avoid repeated expensive MD5 hash calculation for them

Conflicts:
	tycho-p2/tycho-p2-facade/src/main/java/org/eclipse/tycho/p2/facade/internal/ReactorArtifactFacade.java