Warning to save when leaving layout tab
Add/Removed the respective css-marker when the layout is edit/saved; Removed alert
Improve "Export Layout" button interactions:

- Do not mark "Export Layout" button as disabled in the .html, only
  disable it after changes to the layout have been made.

- Trigger "modified.layout" event on column size changes.
Include bootstrap .disabled styles so the disabled state of the "Export Layout" button is visible.
Add test for feature and line in change log (CC @rristow)
Merge pull request #326 from collective/issue_314

Issue 314
Add message on template for empty carousel and enhance testing

Tests still have issues
Fix some JSHint warnings on JS files
Improve css style of Export Layout dialog.
Merge pull request #327 from warpr/issue_306

Issue 306
Merge pull request #329 from warpr/export_layout_dialog_style

Improve css style of Export Layout dialog.