JET-86: Report errors for class objects

idea/testData/checker/ClassObjects.jet

@@ -0,0 +1,30 @@
+namespace Jet86
+
+class A {
+  class object {
+    val x = 1
+  }
+  <error>class object { // error
+    val x = 1
+  }</error>
+}
+
+class B() {
+  val x = 12
+}
+
+object b {
+  <error>class object {
+    val x = 1
+  }</error> // error
+}
+
+val a = A.x
+val c = <error>B</error>.x
+val d = b.<error>x</error>
+
+val s = <error>System</error>  // error
+fun test() {
+  System.out?.println()
+  java.lang.System.out?.println()
+}