added set counting operator, max/min expressions
Merge remote-tracking branch 'origin/master'

Conflicts:
	code/languages/org.clafer.mps/languages/org.clafer.expr/languageModels/editor.mps
	code/languages/org.clafer.mps/languages/org.clafer.expr/languageModels/structure.mps
	code/languages/org.clafer.mps/languages/org.clafer.expr/languageModels/typesystem.mps