Ask for and store Digital Ocean credentials.

I didn't see a way to get their API key by using their username and password. We'll have to ask them for their Client ID and API key in order to make API calls on their behalf.

I thought they had OAuth, but I guess I was wrong. The discussion is here: https://digitalocean.uservoice.com/forums/136585-digital-ocean/suggestions/3493398-support-multiple-api-keys-