Implement ES2015 class feature (part I.) (#2404)

This patch is the first milestone of the implementation of this new language element.

Currently supported:
 - Class statement
 - Class expression
 - Static methods

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

tests/unit-core/test-snapshot.c

@@ -216,7 +216,7 @@ main (void)
     /* Check the snapshot data. Unused bytes should be filled with zeroes */
     const uint8_t expected_data[] =
     {
-      0x4A, 0x52, 0x52, 0x59, 0x0E, 0x00, 0x00, 0x00,
+      0x4A, 0x52, 0x52, 0x59, 0x0F, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x48, 0x00, 0x00, 0x00,
       0x01, 0x00, 0x00, 0x00, 0x18, 0x00, 0x00, 0x00,
       0x03, 0x00, 0x01, 0x00, 0x01, 0x00, 0x01, 0x00,