add ProteinsX dataset classes

[a-r-j]

Reference Issues/PRs

Adds dataloaders for the following built in datasets: #13

• PROTEINS_METAL
• PROTEINS_NUCLEIC
• PROTEINS_LIGANDS
• PROTEINS_NUCLEOTIDES

What does this implement/fix? Explain your changes

What testing did you do to verify the changes in this PR?

• Local testing.

Pull Request Checklist

• Added a note about the modification or contribution to the ./CHANGELOG.md file (if applicable)
• Added appropriate unit test functions in the ./graphein/tests/* directories (if applicable)
• Modify documentation in the corresponding Jupyter Notebook under ./notebooks/ (if applicable)
• Ran python -m py.test tests/ and make sure that all unit tests pass (for small modifications, it might be sufficient to only run the specific test file, e.g., python -m py.test tests/protein/test_graphs.py)
• Checked for style issues by running black . and isort .

[codecov-commenter]

Codecov Report

Merging #204 (2db8ce2) into master (8123f42) will increase coverage by 6.56%.
The diff coverage is 41.53%.

@@            Coverage Diff             @@
##           master     #204      +/-   ##
==========================================
+ Coverage   40.27%   46.83%   +6.56%     
==========================================
  Files          48       93      +45     
  Lines        2811     5647    +2836     
==========================================
+ Hits         1132     2645    +1513     
- Misses       1679     3002    +1323     

Impacted Files	Coverage Δ
graphein/grn/parse_trrust.py	37.77% <ø> (ø)
graphein/ml/datasets/proteins_x.py	0.00% <0.00%> (ø)
graphein/ml/diffusion.py	0.00% <0.00%> (ø)
graphein/ppi/edges.py	100.00% <ø> (ø)
graphein/ppi/graph_metadata.py	0.00% <ø> (ø)
graphein/ppi/graphs.py	54.34% <ø> (ø)
graphein/ppi/parse_biogrid.py	75.00% <ø> (ø)
graphein/ppi/visualisation.py	0.00% <0.00%> (ø)
graphein/protein/analysis.py	0.00% <0.00%> (ø)
graphein/protein/edges/intramolecular.py	22.68% <0.00%> (ø)
... and 87 more

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[sonarcloud]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
2 Security Hotspots
6 Code Smells

No Coverage information
3.5% Duplication

[sonarcloud]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
13 Security Hotspots
6 Code Smells

No Coverage information
3.5% Duplication