Add Category field to OrderSet

add a Category field, which is a Concept, to the OrderSet table to contain the general category the OrderSet is usually used for. If the OrderSet can be multiple categories, the Category Concept could be a Concept of class ConvSet with multiple Concepts in the ConvSet to represent the OrderSet’s more complicated Category. Will also extend OrderSets with attributes to associate the OrderSet’s number of cycles and length of the cycles typical for the regimen.

Please refer to the following Talk thread for more information: https://talk.openmrs.org/t/chemotherapy-ordering-data-design/19133/8