validate.py: show error if "xmllint" is not found

Move file to its parent directory

It seems that it can be used by both engcat and cateng

Add License file (LGPL)

License is LGPL 2 confirmed via:
 * License specified in: https://sourceforge.net/projects/dacco/
 * Mail from Linda Oxnard to the DACCO contributors (Date: Thu, 8 Oct 2020 10:40:31 -0400, Subject: Re: Dacco revival?)
 * FOSDEM talk: https://www.slideshare.net/cpina/dacco (slide 12)

The original CVS repository didn't specify a license for the repository besides in the file: `input/engcat/catSpeakerPublish.xsl`

Fix XML for "teaching" entry