Scope of genes call set to UBKG; proposed endpoints for proteins and genes

[AlanSimmons]

1. With the removal of calls to data from Cells API, the genes endpoint now has scope of UBKG--i.e., it returns all genes in UBKG, not just those relevant to HuBMAP.
2. The SmartAPI specification YAML describes proposed endpoints for:

• proteins
• protein/{id}
• celltypes
• celltype/{id}

[yuanzhou]

Updated change log:

• Refactored routes and controllers to genes-info and genes
• Repackaged pagination information into a Pagination class.
• Refactored for locations of utility scripts, such as neo4j_logic.py and cellsclient.py
• Updated YAML for new pagination object.
• Updated test script.

[yuanzhou]

@AlanSimmons two things to change:

1. since you use underscore-separated fields (approved_name, approved_symbol ...) in the response json payload, we should also do the same with the pagination fields for consistency. Add underscore as a separator for the following fields:

    "itemcount": 43143,
    "itemsperpage": 10,
    "startswith": "",
    "totalpages": 4315

2. To merge this PR, we'll also need to resolve the merge conflicts caused by hs-ontology-api-spec.yaml.

[AlanSimmons]

I changed all references everywhere (parameters, returns, etc.) to use underscores--e.g., starts_with instead of startswith.

[AlanSimmons]

Merge conflicts resolved in YAML file.