Adds the text field credentials as outlets.

We need them as outlets because we wish to use their information to check if
relevent credentials were actually entered.
Adds the incorrect message warning as an outlet to the ViewController.
Adds the functionality of the wrongOrTooManyTriesMessage.

If the button to sign in is clicked and any credential field is empty, there will be a label displaying
that incorrect labels have been entered.
Merge remote-tracking branch 'origin/master'