restored multimodal and mathematical sources

lib/resource-1.0/multimodal/MultimodalGer.gf

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+--# -path=.:present:prelude
+
+concrete MultimodalGer of Multimodal =
+  NounGer,
+--  Verb, 
+  AdjectiveGer,
+  AdverbGer,
+  NumeralGer,
+--  Sentence, 
+--  Question,
+--  Relative,
+--  Conjunction,
+--  Phrase,
+--  Tensed,
+  StructuralGer,
+  DemonstrativeGer,
+  LexiconGer
+  ** {} ;