Treat xml words always as Array

Fixes #440
Extract public parse function in TreebankRetriever
Add a first unit test for TreebankRetriever
More TreebankRetriever specs
Merge pull request #477 from latin-language-toolkit/retriever_fix

TreebankRetriever fix when sentences only contain a single word
Add angular-local-storage through bower
Add LocalStorageModule and configure it
Add morphLocalStorage service
Add angular-local-storage to Gruntfile
Use morphLocalStorage in morph service
Add new forms to localStorage if morphFormCreate
Be more careful when adding forms to localStorage

They cannot have a selected property of true in any case, otherwise we
might end up having two selected forms inside the morph plugin.
Add angular-local-storage to karma config