Ease SHKActionSheet subclassing

* Use `[self alloc]` to allow correctly instantiating subclasses.
* Prefer `instancetype` to `id` (other code should also be updated)
DefaultSHKConfigurator: A better default appName implementation
Minor typo fix
Add `#pragma mark`'s to make it easier to navigate the class' code
Merge pull request #896 from rivera-ernesto/SHKActionSheet_subclassing

Ease SHKActionSheet subclassing
Merge pull request #897 from rivera-ernesto/DefaultSHKConfigurator_improvements

DefaultSHKConfigurator improvements