helios: not exporting helios/set in .amd.json
bump amber dep as now compiled in 0.13 way
fix 5b8f465 for standalone helios development
separate codemirrors in amber and helios:

 - as they use old version (3.x), use name codemirror3;
 - they both have their own codemirror3.amd.json;
 - they both load pieces of CM locally, no reuse;
 - legacy IDE not loaded into Helios window - to promote
   CodeMirror upgrade and preventing clashes.
remove old unused file
amber_lib/showdown -> helios/showdown