JT Beta Key Support, Location/Drive Letter saving, and general fixes

What's New

• JT Beta Key Support by @mattpannella: Now that Jotego is releasing his beta cores publicly (and requiring a beta key to play them), you can just drop the jtbeta.zip file from patreon onto the root of your sd card and run Update All, and it will automatically copy the beta key to the correct folders for the cores that need it. Make sure you don't rename the file, it's going to look for exactly jtbeta.zip
• Remember last used Update Location and Drive Letter: When you select Current Directory or Removable Storage this will be remembered now instead of having to pick every time. The Drive Letter will also use whatever it was last time by default.
• Settings Auto Save when Updating: When you press the Update button your settings on the main screen will be saved Automatically for you just in case you forget to hit the Save button.

What's Changed

• 1.5.7 test by @RetroDriven in #72

Full Changelog: v1.5.6...v1.5.7