#28 Upgrade CodeMirror

Originally at 2014-10-14T15:29:13Z by Herbert Vojčík closed at 2014-11-01T12:37:56Z CodeMirror should be updated to current major version (4) and should be decoupled from amber's internal version of CodeMirror (IOW, do not use 'amber_lib/codemirror' mapping, but either 'codemirror' or 'helios/codemirror').