Launch images for iPhone 6 and 6+

* Targets #19 and #24
* For iOS8 I used `LaunchImage.xib`
* For iOS7 I had to use PNGs, so I recreated them from the xib file (just did a screenshot and removed status bar)
* To support xib for splash screen, I had to use asset catalog for iOS 7 as well
* There's no way (at the moment) to make the PNGs localized, since they're stored in asset catalog which cannot be translated, so I removed language-specific content form them (Breviary, Liturgy of the hours, etc.)