[MRM-980] ability to merge repositories

[MRM-980] ability to merge repositories
submitted by Patti Arachchige Eshan Sudharaka

o added audit logs for merging repos
o fixed merging, merge from staging to managed repo instead of the other way around
o change the repository id in artifact browse from staging one to managed one after the merging is done
o removed unused actions in struts.xml and gave proper name for methods in MergeAction class

additional changes made on top of the patch:
o fixed the title and messages displayed in the merge jsp page
o fixed formatting of merge action

git-svn-id: https://svn.apache.org/repos/asf/archiva/branches/archiva-MRM-980@979534 13f79535-47bb-0310-9956-ffa450edef68