Move projection and geometry to utils/

[matthewhanson]

Is your feature request related to a problem? Please describe.
Suggestion for reorganizing the existing code. While most of the files in core/ deal with modifying or creating STAC items, the geometry and projection modules are utility functions that would be called from elsewhere.

Describe the solution you'd like
Move geometry.py and projection.py to the utils module

Describe alternatives you've considered
Leaving it as is, but it seems arbitrary in that other utility functions are in utils/

[matthewhanson]

Note this could have impact to various stactools submodules that may be using these functions.

[gadomski]

Another alternative would be remove utils/ altogether and just have a flat module space in stactools.core.