Update to Go 1.14 and deploy app to Heroku dyno.

[krashanoff]

This PR turned into a lot more than I anticipated. The gist is that this deploys our backend to a Heroku dyno and prepares it for the backend swap-out. Here's a breakdown of the changes:

• Switch our codebase to Go 1.14.
• Add a Heroku Procfile
• Add a go.mod file for our deps.
• Change the backend to use environment variables for credentials instead of a JSON file.
• Make our Programs use strings instead of time.Time to match the documents currently residing in the database.
• Remove deprecated or otherwise unused functions.
• Deny requests using unsupported methods from CORS.
• More intelligent, mostRecentProgram-aware program deletion in db.HandleDeleteProgram.
• Overhaul endpoint behavior for db.HandleUpdateProgram. We now use uid and pid query parameters to locate the document to update and verify it belongs to the user. Also, since the frontend only ever updates one document at a time, we can just treat the request body as a partial Program object.

[krashanoff]

Alright. This PR turned into a lot more than I anticipated. Here's all that I have done:

• Switch our codebase to Go 1.14.
• Add a Heroku Procfile
• Add a go.mod file for our deps.
• Change the backend to use environment variables for credentials instead of a JSON file.
• Make our Programs use strings instead of time.Time to match the documents currently residing in the database.
• Remove deprecated or otherwise unused functions.
• Deny requests using unsupported methods from CORS.
• More intelligent, mostRecentProgram-aware program deletion in db.HandleDeleteProgram.
• Overhaul endpoint behavior for db.HandleUpdateProgram. We now use uid and pid query parameters to locate the document to update and verify it belongs to the user. Also, since the frontend only ever updates one document at a time, we can just treat the request body as a partial Program object.

I will post a review of the code with commentary later today.

Things are looking in pretty good shape. Sorry for dumping so much information on you all so suddenly. Hope that you're all in good health and had a good finals week. Here's to the start of spring break!

[mattxwang]

Can you do me a quick favour and update the PR title + description with your comments? I think we'll start auto-generating changelogs soon and that would be helpful. Super excited to see all of this happen 😄

[krashanoff]

@malsf21 You got it chief 👍

[krashanoff]

Superceded by #10