GEOMESA-134: DTG field treatment in package object 'index' not safe

Wrap dtg variables in core.index in Options, since the temporal field in...

Also modify FilterToAccumulo to handle these changes.
I agree regarding the warning. 

I also agree regarding the lack of danger in this situation--- I had worried about the row filtering which would have used the non-null time in the index key. However I forgot that the row filtering would not receive the temporal part of the query.