add sgeop as a dependency -- transfer functionality

[jGaboardi]

Add sgeop as a dependency. Then incrementally swapping out functionality here with stuff over there.

• add as dep
  • add sgeop as a dep #178
• geometry.py
  • source geometry.py from sgeop & pin h3<=3.7 #184
• continuity.py
  • source continuity.py from sgeop #186
• nodes.py
  • source nodes.py from sgeop #196
• artifacts.py
  • ...
• simplify.py
  • ...

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• See start filling up testing suite & docstrings sgeop#20