AcceleratorKitProcessor - Decouple "Base Profile" and "Extension Needed"

[sliver007]

The AcceleratorKitProcessor currently expects that the column used for specifying a base profile is also hijacked to indicate whether or not an extension is needed (expects that to be indicated by entering the value "Extension Needed"). In the case that an extension is needed, then the profile created for the data element just uses the corresponding base FHIR resource as it's baseDefinition. This means that we don't support extensions on profiles based on anything other than the base FHIR spec resources.

The notion of whether or not an extension is required for the mapping and what the base profile for the generated profile should be need to be decoupled. A "Extension Required|Needed" column should be added to the spreadsheets and the processor should be made aware of and read this column's value in. The logic in the current "extensionRequired" method should be adjusted to use the value from this new column rather than from the base profile column.