Modify AutoUpdater behavior on macOS.

The AutoUpdater requires that macOS builds be code signed. That is currently not possible.
As a workaround, the autoupdater on mac will now alert users that an update is available and give the option to download the file directly from GitHub.
Closes #16.

app/assets/css/launcher.css

@@ -2099,6 +2099,8 @@ input:checked + .toggleSwitchSlider:before {
 
 /* Update action button styles. */
 #settingsUpdateActionButton {
+    display: flex;
+    flex-direction: column;
     padding-left: 10px;
     background: none;
     border: none;