Issue #2100329 by cosmicdreams: Use \Drupal instead of Drupal to make IDEs and static code analyse tools happy.

Issue #2006282 by joelpittet: Refactor Attribute classes - Cleanup, Security, and Readability and minor performance.

- Patch #1290694 by hefox, tlattimore, c4rl, chx, tim.plunkett, tstoeckler, msonnabaum: provide consistency for attributes and classes arrays provided by template_preprocess().