Add css-writing-modes-4.vim

This syntax is for new spec WD-css-writing-modes-4-20171207.

See also: http://www.w3.org/TR/2017/WD-css-writing-modes-4-20171207/

This commit also removes deferred properties and values from
`css-writing-modes-3.vim`.

test/test.css

@@ -889,8 +889,6 @@
   glyph-orientation-vertical: upright;
   display: plaintext;
   display: sideways;
-  display: sideways-rl;
-  display: sideways-lr;
   display: isolate;
   display: isolate-override;
   display: horizontal-tb;
@@ -898,6 +896,11 @@
   display: vertical-lr;
 }
 
+.writing-modes-4 {
+  display: sideways-rl;
+  display: sideways-lr;
+}
+
 .html5,
 picture,
 rb,