Address beta feedback

* Use signal blue for search box focus outline
* Reduce debounce for draft saves
* Be less aggressive in our scrolling corrections
* Lightbox: Ensure that a tall image is still fully visible
* Fix spell checking after Electron API breaking changes
* Fix link preview image generation
* Message highlight: Move to border in signal blue

test/spellcheck_test.js

@@ -1,6 +1,15 @@
 describe('spellChecker', () => {
   it('should work', () => {
-    assert(window.spellChecker.spellCheck('correct'));
-    assert(!window.spellChecker.spellCheck('fhqwgads'));
+    let result = null;
+
+    window.spellChecker.spellCheck(['correct'], answer => {
+      result = answer;
+    });
+    assert.deepEqual(result, []);
+
+    window.spellChecker.spellCheck(['fhqwgads'], answer => {
+      result = answer;
+    });
+    assert.deepEqual(result, ['fhqwgads']);
   });
 });