Added the ability to update styles from within the player for the next update.
This comes in two forms:
1. Automatic update (disabled by default, must be turned on in the config menu)
When NeoLemmix is started up (currently, only if running an NXP, maybe this should be changed?), updated verisons of styles are checked for, and downloaded if they exist. This is done silently.
2. Manual update
Accessible on the Config menu > "Online Options" tab, this will run a one-off check for updated styles, and inform the user how many (and which) styles were updated.
Currently, this only functions for styles in the user's "styles" folder, and not any in the NXP. While of course the NXP files themself shouldn't be modified, perhaps I should modify this check function to check for newer versions of the styles in the NXP too...