Making library usable in extension targets

[Austinate]

Hi, this PR removes usage of UIApplication`s sharedApplication method to make library usable in extensions targets. (described in #5)

I've run tests and did manual testing for all this cases so nothing should be broken:

• Presenting and dismissing the view controller in both portrait and landscape modes.
• Presenting the view controller, rotating the device and then dismissing from the new orientation.
• Presenting the view controller, then enabling split-screen on an iPad.
• Changing the split-screen window sizes on iPad.

[Austinate]

hm, looks like Travis fail is not actually related to PR changes :(

[TimOliver]

Sorry for the delay! Yeah, I think Travis was complaining because of a wrong Xcode version.

Thanks for that! That looks good! :)