[FEATURE] Description is now a RTE field

The media description can now be edited in a simple rich text editor.
[TASK] Added context sensitive help

The fields of the media element records are now described with context
sensitive help.
[TASK] MP3 and h.246 files are now required

When the user adds a video the h.264 version is a required field.

When the user adds an audio file the MP3 version is a required field.
[TASK] Added layout and metadata

The media is now rendered in a container with the class
tx-html5mediakit-media-container.

Additionally the metadata of a video / audio file is now rendered.