[STORY] Notification - Workflow complete / error

[jsbrittain]

Email notification when:

• [x] Workflow completes a phase
  • [x] Generic email module (https://github.com/kraemer-lab/vneyard/issues/11)
  • manually trigger an email notification module
• [x] #281
  • snakemake will return an error code on failure
  • snakemake also supports onerror handlers: https://snakemake.readthedocs.io/en/v7.0.0/snakefiles/rules.html#onstart-onsuccess-and-onerror-handlers