Add functions to load and calculate coessentiality

[abearab]

• Upload current coessentiality data from https://github.com/kundajelab/coessentiality into CanDI dataverse
• Draft load scripts to load coessentiality data
  • 4fd9dd0
• Use CanDI data handler and define specified python class
• Include coessentiality calculation scripts based on kundajelab/coessentiality & broadinstitute/coessentiality