Drop iOS 7 support

[herzbube]

Dropping iOS 7 support is not an explicit goal, but it might become necessary at some time in the future. This issue tries to track the things that need to be done when the time comes:

• Try again to use UISplitViewController, now that the class supports iPhones. This is impossible if UISplitViewController still has the requirement that it must be the root view controller.
• Use the new Interface Orientation API that was introduced in iOS 8 (see UIViewController class docs)
• Replace UIActionSheet and UIAlertView (which are both deprecated) with UIAlertController
• Replace the multitude of launch screens in images.xcasset with a single .xib file that is capable of adapting to different screen sizes. See the App Distribution Guide, section "Configuring Your Xcode Project for Distribution > Creating a Launch Screen File")
• Look into using UITraitsCollection
• Present modal view controllers using UIPresentationController

Notes:

• 3rdparty libs may use stuff that is deprecated in iOS 8 (e.g. QuincyKit's convenience constructors use NSPropertyListSerialization).
• Dropping iOS 7 support removes the iPhone 4 from the list of supported devices (see this Wikipedia fact sheet)

[herzbube]

With Xcode 7 it is no longer possible to test iOS 7 support because Xcode 7 no longer provides iOS 7 simulators. In fact (according to [1]) the iOS 7 simulator runtime is not even supported anymore by Mac OS X 10.10 (Yosemite), but Xcode 7 only runs on Mac OS X 10.10 or newer (Xcode 7.3 which I use even requires Mac OS X 10.11).

[1] http://stackoverflow.com/a/32974149/1054378

[herzbube]

iOS 8 and later uses a launch screen storyboard during application startup, replacing the old static launch images. As soon as support for iOS 7 is removed, the currently existing launch images can also be removed.

[herzbube]

The final straw: The new version of Cocoa Lumberjack (2.3.0) sets the deployment target to 8.0, which causes linker errors while we remain at 7.0.

[herzbube]

The Cocoa Lumberjack build target CocoaLumberjack-iOS sets the deployment target to 8.0. However, as it turns out we must use build target CocoaLumberjack-iOS-Static, and that sets the deployment target to 8.1. The reason for the difference between Cocoa Lumberjack build targets is unknown, but we follow suit and set our own deployment target to 8.1 to prevent linker warnings.