[Organic Maps] Add ability to store map files in OBB directory on Android

⚠ Have you searched for similar, already existing issues? yes **Is your feature request related to a problem? Please describe.** Hi, It is not always convenient to use the built-in map downloader. Sometimes it is easier to keep a local mirror of the entire world set and copy mwm to the app as needed. The current functionality does not allow you to copy maps from the outside without rooting the device (more precisely, you can, but this is a very hacky method with adb and chmod). It would be very nice to have a standard way to copy map files into, ahem, the inside of the app - for example, right on a trip from a slow microSD, which contains the whole world, to internal fast memory, which contains the current country or continent. It is also faster and more convenient to update the entire world this way, and will allow you to do this both through adb and through any file manager in android. Добрый день, Не всегда удобно пользоваться встроенной скачивалкой карт. Иногда проще держать