Image aspect ratio (#1665)

* Allow user to specify an aspect ratio for various images

* added a comment on what is supported

* fixed typo

* Fixed lint and test errors

src/common/util/parse-aspect-ratio.js

@@ -0,0 +1,24 @@
+export default function parseAspectRatio(input) {
+  // Handle 16x9, 16:9, 1.78x1, 1.78:1, 1.78
+  // Ignore everything else
+  function parseOrThrow(number) {
+    const parsed = parseFloat(number);
+    if (isNaN(parsed)) throw new Error(`${number} is not a number`);
+    return parsed;
+  }
+  try {
+    if (input) {
+      const arr = input.replace(':', 'x').split('x');
+      if (arr.length === 0) {
+        return null;
+      }
+
+      return arr.length === 1 ?
+        { w: parseOrThrow(arr[0]), h: 1 } :
+        { w: parseOrThrow(arr[0]), h: parseOrThrow(arr[1]) };
+    }
+  } catch (err) {
+    // Ignore the error
+  }
+  return null;
+}