Updated CodeMirror to v3.16.0

Libraries from:
https://github.com/marijnh/CodeMirror/

Version info from:
https://github.com/marijnh/CodeMirror/blob/master/bower.json

JS minified with uglify and CSS minified with sqwish

Included addon, mode and theme folders absent from v3.12.0. The mode
folders are needed because they contain the syntax highlighting rules
for each file format, without which CM isn't much use.