cligs/textbox: Almost Summer Release

In this release, the existing collections have been updated to be more consistent and to improve validation. The main changes are:

• The keywords in the text classification section of the TEI header have been normalized and hierarchized in all the collections.
• A TEI keyword list and a schematron file controlling term values have been created for each collection.
• The schemas for TEI master files and annotated versions have been merged to a single, common schema for all TEI files. See also https://github.com/cligs/reference where the schema files are hosted.
• In the schema and TEI files, a CLiGS namespace has been introduced for:
  • a CLiGS specific attribute importance used to indicate the importance of each genre assignment in case of several different assignments
  • non-TEI sentence and word level attributes resulting from NLP annotations with FreeLing
• Folder names have been adjusted to be consistent for all collections in the textbox.
• For details, see the version history in the "next" branch: https://github.com/cligs/textbox/commits/next.