Add initial Two Factor Support

[solidnerd]

This adds support for Two Factor Authentication when it's enabled to be able to login into an gitlab instance.

Fixes #10

Signed-off-by: solidnerd [email protected]

[solidnerd]

CLI Output looks like the following:

WARN[0000] Scopes can't be blank setting by default --api
INFO[0000] Found Two Factor Authentication
INFO[0000] Please Provide a valid OTP Token to login:
773059
yRwTkroLMxJx7MDMUy6g

[coveralls]

Coverage decreased (-1.9%) to 46.503% when pulling e8436c59514e0c7d9fa80f62b13e92b2398faa50 on feature-2fa-login into f4052c2595083c1352d4674a33772f5ab165990b on master.