Added possibility to import *.perfdatarepo and to specify more then 1 ImportDeclaration

edu.kit.ipd.descartes.mm.adaptation.sta.ui/plugin.xml

...scartes/ui/contentassist/antlr/internal/InternalStaLang.g

...i/contentassist/antlr/internal/InternalStaLangParser.java

...tation.sta/src-gen/edu/kit/ipd/descartes/StaLang.xtextbin

...kit/ipd/descartes/parser/antlr/internal/InternalStaLang.g

...escartes/parser/antlr/internal/InternalStaLangParser.java

...escartes/serializer/AbstractStaLangSemanticSequencer.java

.../edu/kit/ipd/descartes/services/StaLangGrammarAccess.java

...sta/src/edu/kit/ipd/descartes/mm/adaptation/StaLang.xtext