Gave the ability to have zonal summary use cached results.

- Added a .cached method to DataSourceLike that caches the results
  of the elements on the local machine.
- Refactored zonal summary methods to take in cached results
  to be used on the full tile intersections.
add double support to max focal operation
add double support to min focal operation
add double support to standard deviation focal operation
add double support to sum focal operation
Merge pull request #671 from Markko/FocalDouble

add missing double support to Focal operations issue: 630