Generalized all ARV regimen code so that it can work easily with TB regimens etc
* Generalized all regimen code to use a category argument
* Regimen now represents a prescribable regimen of drugs, rather than the orders
* Existing Regimen becomes RegimenOrder and RegimenHistory becomes RegimenOrderHistory
* Made re-usable Regimen field with String->Regimen converter
* Improved regimenEditor page validation
  + Checks that there is at least one component in a regimen
  + Checks that there are no incomplete components
  + Requires change reason for stops and changes