Default permissions, CodeMirror editor improvements and bugfixes

Today's update (a1a3d64) brings with it the following changes:

New features

It's now possible to save a set of default permissions which will be applied whenever you create new objects or containers.
- These permissions are also applied when you unpack zip files or upload files directly.
- When you create voice recordings using the recorder app these default permissions are not applied.
- If you unpack a zip file over existing content the permissions of the existing content will not be modified, although the content will be.
A button has been added to the metadata tab of the container and object editor to allow for generation of the LOM XML content. This should make it easier to add additional titles in other languages.
A help feature has been added to the CodeMirror editor. Press F1 while the cursor is inside the editor to access the help feature.
It's now possible to randomize and sort lines in the CodeMirror editor. You use the keys F8 and F9 respectively to perform these actions.

The current_timestamp template function now returns a DateTime instance instead of a string, allowing for more date math and other behavior. The returned timestamp always has the timezone set to UTC, instead of using local timezone. This does mean that users will see timestamps with an offset from what they're used to, but this can't be improved unless we have some way of gathering the time zone from the browser and storing it in the session (or cookies).
A lot of the behavior around adding and removing permissions to containers and objects has been changed. It should now be more consistent all over.
Some strings in the Spanish translation was updated.

When the create_response template function was used and the CodeMirror editor was used, saving and sending in content was impossible. This has now been fixed.
HTTP redirects didn't include a CORS header, even if one was specified for the site. This has been fixed.