Revert "Document can only have supported language"

This reverts commit 1c351f63ad227ee1c9be1a218853f63be5358664.

We'll handle the bad language codes in the DB manually during deployment
Set default language to "eng"
Add default to lib/dc/language.rb

Conflicts:
	lib/dc/language.rb
OCR language is the same as just "language" now

Since we're now using 3 character codes, it should match up to what
tesseract expects