Extend data wrangler factory so that it can instantiate data wranglers not included with lmpy

[cjgrady]

Currently, the factory cannot instantiate data wranglers defined outside of lmpy. However, there are use cases where new data wranglers or sublcasses would be created outside of lmpy and we need to support those.

Add an optional parameter the wranger configuration indicating what module the wrangler to create is contained in and use that when it is supplied.