Add instance method `String Config.getBackEndName()`

  * This method enables a config instance to respond to which backend it
  belongs even before the backend instance gets created.  After adding
  jvstm-common, this became necessary to enable MultiConfig to continue to
  operate: It uses the backend name to map the configuration, and this is done
  before the backend instance exists.
set forkCount as a property

  * To play on the safe side use forkCount=1 as default.  This can be changed
    via command line, e.g. `-DforkCount=1.5C`.

  * This commit restores lost commit
    (383bd8ee0ee4168ff1d69864a860971ec1c1726f) when renaming folders

Conflicts:
	parent/pom.xml
[test-backend-jvstm-common] Fix: Restore jvstm-infinispan dependency to ff-maven-plugin