Added STextHoverStyleSheet.css to binary build

plugins/org.yakindu.sct.model.stext.ui/build.properties

@@ -2,4 +2,6 @@ source.. = src/,\
           src-gen/
 bin.includes = META-INF/,\
                .,\
-               plugin.xml
+               plugin.xml,\
+               StextHoverStyleSheet.css
+