Allow specification of APP_ID, SECRET, DOMAIN, ENDPOINT per account

[apiv]

I'd like to be able to manage my github enterprise and github.com repos on the same strider instance. As of right now, I can only do one or the other (since the config is locked in by the environment config).

What I'd like to do is add some additional fields to the "Add Account" form. These fields can be hidden by default, shown when a user clicks an "Advanced Options" button. These fields would default to the values defined in the environment variables, but would allow the user to override them in the form if they want:

• APP_ID
• SECRET
• DOMAIN
• ENDPOINT

[knownasilya]

Would totally take a PR :+1: