Improved voice recorder, file manager and much more

Today's update (f26f6ff) brings the following changes:

New features

It is now possible to use voice recording exercises in CEFR speech and conversation categories.
In the CEFR test, it's now possible to attach the voice recordings in the final report that is sent by email.
The recorder() template function now supports saving as well. It is also possible to specify title, description, and if the recording should be accessible for all users. It is also possible to specify which document the recording originated from and where to redirect on success. You can also hide specific form fields if wanted.
Added boolean config variable hide_supervisor_info. If set to a true value, the error message about missing supervisor should no longer display.
When uploading JSON files, they should be detected as application/json and set to UTF8 encoding.

Cleaned up and modernized the file manager user interface significantly.
The Flash-based voice recorder has been almost completely rewritten, and should be much more robust now. It should also have slightly better audio quality.
The large audio player used when playing back WAV and MP3 files now shows time elapsed and has a slider you can use to move around during playback.
When errors occur, the resulting page was usually returned with HTTP status 200 and some error message. The HTTP status code used is now the same as the error message's error code. This could impact JavaScripts and apps, so make sure you carefully test them to ensure they still work.
Group search now allows searching for just a single letter.
It is now possible to see all of the icons in all of the themes available in the icon list.
Made use of the Java-based voice recorder ListenUp slightly more robust.

Improved the speed of the file manager by using an AJAX request for the group search.
The Site folders user interface should be significantly faster.
Icon rendering should be substantially faster, as all icon information is preloaded when the server is started.
Code improvements should generally improve data access slightly everywhere, making especially large lists and tables faster.

Ensure UTF8 content is handled properly when updating object content.
Serialized XML and HTML in configuration variables should now output correctly in XML response mode.
Use locale-dependent title of containers and objects everywhere if specified. In some situations the primary title was used instead of the localized one.
Image thumbnails should now render with the proper aspect in object edit view.
Fixed a problem that occurred if a template had an error, the line number shown in the error message was off-by-one.