Merge lastest

1. Method changePOS has been finished.
2. Added a new table modifierTable. Add ModifierTableValue class, which represents value in the table.
3. Method discount finished. Not tested. Added a new table discountedTable, and added a new class DiscountedKey to represent the key of the table.
4. Method getParentSentenceTag has been finished.
5. Method getMTFromParentTag has been finished. All test cases added. Now it has been fully tested.
6. Method tagSentWithMT has been finished.
7. Added a constructor in Treatment class. Changed the input of populateSents method from a folder to a list of treatments, so it can now be tested separately.