[JENKINS-12495] Make FeatureBranchProperty serializable, move upstream location retrieval on master side.
Merge branch 'master' into jenkins-12495

Conflicts:
	src/main/java/jenkins/plugins/svnmerge/FeatureBranchProperty.java
Merge pull request #11 from jenkinsci/jenkins-12495

[FIXED JENKINS-12495] Support rebase/integrate actions on slave