Expose the documentStore through state.documents()
Expose parsed xml documents trough the store
Extract additional info in the treebankRetriever
Add save button
Add persister
Add persister configuration in staging2
Move treebankPersister to services folder
Add configurator.getPersisters()
Add persisters to main scope

This is just a temporary solution, check the comments in the MainCtrl.
Start to add spec for TreebankPersister
Add persisters to staging conf
Add arethusaUtil.json2xml()
Log a success message in mainCtrl
Add update fns to TreebankPersister
Whitespace typo
Minor refactoring
Extract adding of sentences to navigator
Update persister to use new navigator object
Add docIdentifier to identify doc in the store
Minor formatting