Disable autocorrect on username & password fields.

I updated both username and password fields to skip autocorrection. I would
think that setting a field to "secure" would disable this by default but I was
unable to find an affirming statement in the docs so assumed it would be better
to play it safe and be specific.
Merge pull request #157 from lliss/topic/username-autocorrect

Disable autocorrect on username & password fields.