Implement 2-factor authentication during login (by email)

[aduffeck]

This commit handles the case where 2fa is required by the server.

An email code is requested from the server which can then be entered on the command line to complete the 2fa flow.

Fixes #37, #46 and #55.

[rbignon]

Hello,

Thank you for your contribution. I have no way to test it, but it seems good (and at worst it wouldn't break anything if it does not work).

[securitygeneration]

@aduffeck I'm getting an error trying to log in to an account with 2FA:

Requesting 2fa code...
Enter auth code: Traceback (most recent call last):
  File "/usr/src/app/./doctoshotgun.py", line 627, in <module>
    sys.exit(Application().main())
  File "/usr/src/app/./doctoshotgun.py", line 529, in main
    if not docto.do_login():
  File "/usr/src/app/./doctoshotgun.py", line 215, in do_login
    code = input("Enter auth code: ")
EOFError: EOF when reading a line

[aduffeck]

@securitygeneration how do you run doctoshotgun? It looks like it's something non-interactive that doesn't support input?

[securitygeneration]

I'm running it via Docker (basically following the readme instructions)

[aduffeck]

@securitygeneration I see. can you please try docker run -it instead of just docker run? That should fix the problem for you.

I'll prepare a pull request to adapt the readme accordingly

[aduffeck]

I just created the readme PR at #77

[securitygeneration]

Yep, the -it runs it interactive, thanks :)