Implement spherical and geographic strategies in order to maintain
backward compatibility. Even though dummy legacy strategy is returned.
Add centroid tests for undefined CS.
Also is_simple, is_valid and extensions like dissolve and nsphere relops.
Add umbrella strategies:
- relate: used in setops, relops, buffer, is_xxx, dissolve, etc.
- index: used in rtree
- io: used in wkt read/write and extensions/shapefile
Replace `point_box_by_side` agnostic strategy with CS-specific strategies.
Fix passing of strategies (no defaults when user-defined strategy is
passed) in places like buffer and distance.
Alter tests accordingly.
