DevTools: Make WebInspector.ConsoleMessage a pure model entity with no UI features

WebInspector.ConsoleMessage used to combine both model and UI aspects, thereby
violating basic architectural principles.

ConsoleMessage.setMessageElement() has been removed because of this, and
we also don't see great value in the profile name linkification.

R=eustas, pfeldman

Review URL: https://codereview.chromium.org/173693003

git-svn-id: svn://svn.chromium.org/blink/trunk@167880 bbb929c8-8fbe-4397-9dbb-9b2b20218538