Fix editor's lack of cooperation as a flexbox item

Two main changes: First, use absolute position left/right/top/bottom of 0 as a hack to achieve 100% width and height of the flexbox that contains the gutter and scroll view when it is inside an editor that is itself a flexbox item. Now we don't rely on the editor having a definite height because of the absolute positioning. This seemed to confuse the newer flexbox implementation, so I fell back to the old one which seems to work better than last time I tried it for this purpose (it had rendering artifacts before)

static/editor.css

@@ -9,13 +9,17 @@
   position: relative;
 }
 
-
 .editor.mini {
   height: auto;
 }
 
 .editor .flexbox {
-  display: -webkit-flexbox;
+  display: -webkit-box;
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  left: 0;
+  right: 0;
 }
 
 .editor .gutter {
@@ -51,8 +55,7 @@
 .editor .scroll-view {
   overflow-x: auto;
   overflow-y: hidden;
-  width: -webkit-flex(1);
-  height: 100%;
+  -webkit-box-flex: 1;
 }
 
 .editor.mini .scroll-view {