MacOS: Make auto-updates work instead of prompting the user to update by themselves

[amo13]

On MacOS, auto-updates fail because the application .app package is read-only. Therefore, the binary residing in a subfolder cannot be overwritten.

Another thing that could be improved for Mac users is the location of the folder containing the log, the downloaded binaries and the downloaded roms, TWRP images, and other zips for flashing. Currently, on MacOS, it is simply put into the user's Downloads folder. A better approach would be to create and use a folder relative to the location of the .app application package, just like on Windows and Linux. This has been discussed here and the described workaround has been chosen until a better solution can be found.