Change Operation to modify xml_node instead of xml_document
Add static consts to identify xml tags for tasks and other data
executeTransaction now receives xml_node instead of xml_document
Add getter for tasks and data node
getAllTask and onTransactionCommit make use tasks node getter
XML Handler getters now require xml_document as parameter

For onTransactionCommit temp xml_document
Modify test to adhere to the changes in xml structure, add some explanation
Add BranchOperation
Add test for BranchOperation
Completely refactor getTasksNode and getDatanode
Refactor out constants into separate constants files
getAllTasks in internal datastore is replaced with a generic getAll
Change API to make use of the generic getAll, add getAllResources
Fix internal test to adhere to the changes
Merge pull request #233 from digawp/last-id

Preparation to store last ID in xml file