Remove deprecated and dead code, cleanup obvious things

First of probably a few refactoring commits.

This PR:
1. Remove instances of `viewDidUnload` and place appropriate calls in `dealloc` or `didReceiveMemoryWarning`. 
2. Clean up obvious things that are deprecated: eg remove actionsheet alternatives for when we have UIActivity -- no longer need to check for the existence since iOS 6.
3. Remove random unused code
4. Stick to coding style in https://github.com/wordpress-mobile/WordPress-iOS/wiki/WordPress-for-iOS-Style-Guide (except for the newline for a curly brace)

Related issue: #573