Generate equals/hashCode(): Enable for classes without properties

Also:
- forbid for enum classes
- use javaClass.hashCode() instead of 0 if class has no properties

 #KT-18418 Fixed

idea/testData/codeInsight/generate/equalsWithHashCode/noVars.kt

@@ -1,4 +1,3 @@
-// NOT_APPLICABLE
 class A {<caret>
     fun foo() {