Fixing issue with creating unessacry null demand and split ratios values.  Plus removed unnessary methods from dynamic demand set and added additional sensor serialize unit test.
Merge branch 'dev' of github.com:calpath/model-objects into dev
Fixing issue with getting correct demands and split ratios when start time is not 0 by adding subtraction of start time from offset time when returning demand at particular time.
Merge pull request #136 from mnjuhn/dev

Dev