Fix Mime Type Helper on Multiple Extensions

Fix mime type helper on multiple extensions for the same mime type.
Previously if there were multiple extensions the last one would be the
only one

- Reverse mime type array
- Flip methods
- Add phpdoc
Merge pull request #1365 from mkly/fix_mime_type_helper_on_mutliple_extensions

Fix Mime Type Helper on Multiple Extensions
restored case insensitivity, corrected some naming and comments