Adds the following JS libraries:
* CodeMirror - extensible text editor
* FileSaver - shim for saving files
* require - dependency resolver and module loader
Signed-off-by: Nick Clemens <nick@quecheelibrary.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
