Only Email Steam Guard variant supported

[Programie]

A change in the handling of the Steam Guard Code in Spectrum2 results in an error logged to the backend log (Unhandled request input. primary=Steam two-factor authentication) if Steam Guard with the Steam Mobile App is enabled.

libpurple-steam sends different input requests depending on the enabled Steam Guard variant. For mail is "Set your Steam Guard Code" which also matches the current implementation in Spectrum2. But for the Steam Mobile App the input request is called "Steam two-factor authentication".

See libsteam.c (Email variant) and libsteam.c (Steam App variant).

Previously I was able to successfully login using Steam Guard for the Steam Mobile App. This behavior has been changed in #302.

I guess Spectrum2 should support both variants.