Update version of spock to 0.7-groovy-2.0. @TestCategory works fluent with current spock version

Update version of spock to 0.7-groovy-2.0 , as of this version as improved Junit compatibility

-  org.junit.internal.AssumptionViolatedException are now recognized by spock (as of Junit @Rule)
-  Bumping groovy and gmaven versions accordingly
-- See http://docs.spockframework.org/en/spock-0.7-groovy-2.0/new_and_noteworthy.html
Java 7 runtime is required
Project update to 3.0-SNAPSHOT (not backward compatible)