Latin grammar: clean up and update

This patch removes all superfluous files from the directory, especially the
binary files in the doc folder. They are still available in the git
repository http://github.com/daherb/GF-latin which is still the main
repository for the development of the latin grammar.
The GF files are updated to a state close to the one at the end of the GF
Summer School 2015 where they were extended to support the MUSTE grammar.

src/latin/GrammarLat.gf

@@ -7,11 +7,12 @@ concrete GrammarLat of Grammar =
   AdverbLat,
   NumeralLat,
   SentenceLat,
---  QuestionLat,
+  QuestionLat,
 --  RelativeLat,
 --  ConjunctionLat,
   PhraseLat,
   TextX,
+  TenseX,
   StructuralLat
 --  IdiomLat
   ** {