Load bigg data

[nwlandry]

This addresses #376. This PR

• Moves the json from url functions to the utilities and slims down the xgi_data module
• Adds a bigg_data module.

[codecov]

Codecov Report

Patch coverage: 92.42% and project coverage change: -0.10 ⚠️

Comparison is base (5b2cc16) 91.11% compared to head (004c199) 91.02%.

❗ Current head 004c199 differs from pull request most recent head bd3c1da. Consider uploading reports for the commit bd3c1da to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #384      +/-   ##
==========================================
- Coverage   91.11%   91.02%   -0.10%     
==========================================
  Files          46       47       +1     
  Lines        3771     3878     +107     
==========================================
+ Hits         3436     3530      +94     
- Misses        335      348      +13     

Impacted Files	Coverage Δ
xgi/algorithms/centrality.py	97.39% <ø> (ø)
xgi/stats/dinodestats.py	82.35% <ø> (-0.99%)	⬇️
xgi/utils/utilities.py	93.05% <73.68%> (-6.95%)	⬇️
xgi/readwrite/__init__.py	100.00% <100.00%> (ø)
xgi/readwrite/bigg_data.py	100.00% <100.00%> (ø)
xgi/readwrite/xgi_data.py	100.00% <100.00%> (+6.00%)	⬆️

... and 2 files with indirect coverage changes

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