Disabling submit button until all questions have been answered and fix back button;

Closes #138 (closed). Disable the submit button within GuestQuestionnaireFragment.java until all questions have been answered.

FIXED ALTERNATIVELY #138 (closed): Instead of disabling before all questions have been answered, I left it enabled but denied submission and added an AlertDialog that pops up and informs the guest if there is any missing fields in their submission.

TESTING #138 (closed): Navigate to the guest visit scanner in the app (Guest Forms -> Guest Visit Check In (Local Database)). Scan a Code 39 barcode and press the Confirm Scan button. When you get to the GuestScanConfirmationFragment press the Confirm button. Press the Submit button without answering any questions. There should now be a dialog that pops up and informs you that there is missing fields. Now, answer all of the fields then press the Submit button again. Make sure all of the input fields are disabled and that the Submit button is disabled. Make sure you see your answers in the log. Also, test the rotation to make sure the input fields are being saved properly.

Closes #135 (closed). When in the GuestQuestionnaireFragment when the app is running. If you rotate the screen twice then press the back button, the GuestScanConfirmationFragment doesn't get saved properly and displays the view that says "NEST Guest Not Found!"

TESTING #135 (closed): Navigate to the guest visit scanner in the app (Guest Forms -> Guest Visit Check In (Local Database)). Scan a Code 39 barcode and press the Confirm Scan button. When you get to the GuestScanConfirmationFragment press the Confirm button. Press the Back button and confirm that it has brought you back to the scanner.

NOTE #135 (closed): I made the back button take the user back to the scanner, since there is no real point of returning to the confirmation fragment.