Handle Passphrase Request When Using ssh URLs

[jmwright]

This is broken out from issue #31 so that it can be addressed separately. If a user has a passphrase set for their ssh key, it will be requested when they try to upload/refactor. On some OSes this is handled properly and the GUI will present them with a passphrase dialog when needed. Sometimes though it gets swallowed up, leading to a hang or authentication error that the user can't do anything with. This is a temporary work-around, but I think there are ways to forward that ask to other utilities. This could be tied in with a more secure way to handle the passwords for https. I'm not sure yet.

Other related links:

• https://stackoverflow.com/a/52356592/2174937
• https://git-scm.com/docs/gitcredentials.html