Merge pull request #462 from joshmarcus/topic/tiled_local

Local operations act transparently on tiled rasters.
Unify focal operations on tiled and untiled rasters.

This commit removes the need to use TileFocalOp when applying focal operations
to tiled rasters.  Focal operations now extend FocalOperation[Raster] with CanTile.
The public analysis area interface has been removed from the base classes.

The current mechanism uses reflection.  I have an initial implementation of an alternate
strategy, but this checkin extends the current strategy to simplify the API for the user.