Refactor readers for better di (#457)

* Refactor readers to get a proper DI

Similar to what was done with writers, readers also needed to be updated to match the new way of doing things.
This commits promotes a better DI (factories, injection through constructors).

* Escapers should not be singletons

Instead, they should be proper object that can be injected where needed.

src/Spout/Reader/SheetInterface.php

@@ -12,7 +12,7 @@ interface SheetInterface
     /**
      * Returns an iterator to iterate over the sheet's rows.
      *
-     * @return \Iterator
+     * @return IteratorInterface
      */
     public function getRowIterator();
 }