Fix: Create resized directory when it does not exists

Closes #522
Unindent doc block following CS
ImageHelper: Method extraction for readability + DRYness

- Docblock fixes
- Variable renames
- New protected methods: _resize() and _setupTransparency()
Merge branch '2.0-image-helper'

* 2.0-image-helper:
  ImageHelper: Method extraction for readability + DRYness
  Unindent doc block following CS
  Fix: Create resized directory when it does not exists