delete splits when transaction is saved.

Currently, the edit of transaction and each split are saved when the transaction is saved (when the save button is clicked in the TransactionFormFragment), except that the splits deleted in the splits view are deleted when the split view exits.

When the splits are saved (resulting in some splits deleted, others edited), but the transaction is not saved, it will result in a transaction with some deleted splits while no other splits change. However, when the transaction is not saved, nothing should change in the transaction, including the deleted splits.

This pull request would make all edits/deletions to splits and edition to transaction to be saved when the save button is clicked in the transactionFormFragment.