Add iOS version check and update notification

@agreer said:

@aconnell this would be a low-priority thing but if it's a small lift we may want to consider it sooner vs later -- are we able to check their iOS and pop up a notification if their OS is older than a certain threshold?

Something like "hey due to the outdated OS you're running, you might experience lag and/or other performance issues using the Ludex app. Update your OS for the best experience!