* Fix ASPrimitiveTraitCollection initialization on iOS 9.
Add nil-value checks for preferredContentSizeCategory.
* * Mark -[ASTraitCollection init] as deprecated.
* Mark [ASViewController overrideDisplayTraitsWithWindowSize] as deprecated.
Code review changes:
* Remove unneeded nonnull annotations
* Add null check in ASTraitCollection constructor implementation
* Codestyle
* Add some documentation about ASPrimitiveTraitCollection vs ASTraitCollection usage
* Rename safeContentSizeCategory to AS_safeContentSizeCategory.
Remove safePrimitiveContentSizeCategory in favour of AS_safeContentSizeCategory.