Optimize bundle size, and drop its support for J2ME's Opera (layout doesn't support small screens anyway)

Signed-off-by: Egor Savkin <es@m-labs.hk>

package.json

@@ -35,8 +35,16 @@
   },
   "babel": {
     "presets": [
-      "@babel/preset-env",
-      "@babel/preset-react"
+      "@babel/preset-react",
+      ["@babel/preset-env", {
+        "targets": {
+          "browsers": [
+            ">0.25%",
+            "not dead",
+            "not op_mini all"
+          ]
+        }
+      }]
     ]
   }
 }