UI: Make minor changes in buttons and error messages of tutorial

[catloversg]

These changes were suggested on Discord:

• or click 'EXIT': Wrong text. "EXIT" button was renamed.
• Put "Bad command. Please follow the tutorial" to a constant.

I also make these changes:

• Change capitalization of "Skip" button and "Finish" button. We rarely use ALL-CAPS for button description.
• Show the player how to replay the tutorial.

[d0sboots]

I'm gonna suggest "Exit Tutorial" instead of "Skip Tutorial," because "skip" sounds like it might just be skipping the current action or part of the tutorial instead of the entire thing.