Miscellaneous additions and changes

- Guided introduction added to training mode
- Users that have not tried training mode will be alerted via an alert view when they go to the 'Begin' mode menu. The alert will stop being shown once they've gone through the introduction in training mode.
- Swapped yes and no button positions
- Images can now be dragged horizontally
- Image scaling via the pinch gesture has been improved
- A 'Submission Successful' view is now shown after an image description is submitted
- More back button changes
- Removed sign in from the main menu
- 'About' shows about text
- Several small animation changes throughout the app
- Changed arrow/cursor keys on the keyboard into arrows
- Added several new keys to the keyboard