iOS-specific "iframe loader" HTML pre-processor (epubReadingSystem injection + MathJax bootstrapper)

Follow-up to OSX equivalent:
https://github.com/readium/SDKLauncher-OSX/pull/14

Note that the iOS app launcher uses the readium-sdk RDServices, so make sure to checkout feature/htmlInject there as well: https://github.com/readium/readium-sdk/pull/102