First (hopefully) working release

How the mod system works:
There are 2 additional files in shared_prefs: installedmods.xml and one that's named after the mod id.
The installedmods file has one string value called "current", which stores the name (mod_id) of the currently installed mod. The file named after the mod id has one int value called "version", which stores the version as defined in appSettings.json. Currently, files are only extracted if either the mod id hasn't been set yet or if the mod id matches the mod id of the new mod and the version is lower than the new version.