consistent img naming convention and organization

edit of English version
(intention is to make process of creating a new translation easier)

images:
- consistent use of reference style image syntax in chapters
- language subfolder within images folder
- file naming convention:
	en_beg_[two digit chapter #]_
	[chapter name based on permalink]_
	image[two digit # code]_
	[image name based on image reference id]

other:
- link in CONTRIBUTING.md updated to skip a redirect