add interface to write string metadata with helper tool


git-svn-id: svn+ssh://svn.cern.ch/reps/atlasoff/Database/AthenaRoot/AthenaRootComps/trunk@564537 4525493e-7705-40b1-a816-d608a930855b
see changelog


git-svn-id: svn+ssh://svn.cern.ch/reps/atlasoff/Database/AthenaRoot/AthenaRootComps/trunk@564538 4525493e-7705-40b1-a816-d608a930855b
cleanup debug messages


git-svn-id: svn+ssh://svn.cern.ch/reps/atlasoff/Database/AthenaRoot/AthenaRootComps/trunk@564565 4525493e-7705-40b1-a816-d608a930855b