TRUNK-4445 Added support for custom dosing type for DrugOrders. Changed the current dosing type enum to a string, while keeping the support for SIMPLE and FREE_TEXT dosing types using constants

TRUNK-4445 Made doing type of type class <? extends dosinginstructions>

TRUNK-4445 Adding validation to the the dosing instructions class, and removing them from drugordervalidator

TRUNK-4445 changing the shoulds and verifies in the required places, renamed dosinginstructionsobject to dosinginstructionsinstance. Catching exceptions inside the getter now. Updated the message.properties with suitable messages for dosingIntructions Free Text

Adding java doc for DosingInstructions and removing unused import

Follow up to clean up unit tests and the liquibase update file   - TRUNK-4445

Conflicts:
	api/src/main/resources/liquibase-update-to-latest.xml
	api/src/test/resources/org/openmrs/include/standardTestDataset.xml