BUG / Housekeeping of Widget code

- TagCloudWidget not wrapped with `if(class_exists('Widget'))` check for dependency module
- Default titles for RSS Widget and TagCloudWidget not being translated. Added to en.yml (missing getlocalization for blog?)
- Fixed poor indentation, and excessive line length (scrutinizer errors)
- Removal of several blank `private static $relation = array()` that added no value
- Fix of many 'R S S' typos in lang. Should be 'RSS'
- Missing PHPDoc for widget classes
- Fixed missing EOL and removed closing ?> from php files for consistency

I noticed that http://www.getlocalization.com/silverstripe_blog/ doesn't have any actual strings loaded against it. Do I need to do some work here to populate getlocalization for the blog, or should I just leave it?