Support custom DosingTypes

The current orderservice API supports only two types of order types - SIMPLE and FREE_TEXT. This ticket proposes to change this to support multiple order types.

Changes

1- Make DosingType a String varchar(255) with public constants for existing values - SIMPLE and FREE_TEXT.
2- The dosingType fields should be set to their respective java class names i.e org.openmrs.SimpleDosingInstructions and org.openmrs.FreeTextDosingInstructions for SIMPLE and FREE_TEXT respectively.

Based of discussion here.

Relevant section in notes:

2. handle variable dose - 3 times a day, 4 times a day
"1 2 1" -> "one in the morning, two in the afternoon, one in the evening"
This is done through dose instruction type i.e. we need a new DosingType
Five special dose types are common: variable, alternate day (like warfarin 2mg on odd days and 3mg on even days), taper, titrate, sliding scale. These benefit from a special handler, otherwise the user experience is pretty painful. Titrate can be well handled just with instructions.

DEV NOTES:

• Find the existing changesets with ids 201312141400-TRUNK-4126 and 201312141400-TRUNK-4127, make sure they set the correct column values and datatype [varchar(255)]