DevTools: move cmdevtools file out of cm/ folder.

File cmdevtools.css is not a part of codemirror distribution - it
customizes editor look & feel of the devtools editor.

R=apavlov

Review URL: https://codereview.chromium.org/362543002

git-svn-id: svn://svn.chromium.org/blink/trunk@177223 bbb929c8-8fbe-4397-9dbb-9b2b20218538