Change subviews' properties to be weak

They don't need to be strong, because they're referenced by their superview.
This change simplifies the process of tearing down the view in dismissAnimated:duration:completion: (remember that the action sheet can be shown more than once!)
Refactor setting up subviews

Conditionals were removed because methods:
- setUpNewWindow
- setUpBlurredBackgroundWithSnapshot:
- setUpCancelButton
- setUpTableView

won't be called more than once if the action sheet is still visible on the screen.
Fix the order of methods
Fix possible fractional view sizes