DevTools: Rename WI.ModuleManager to Runtime

This is a preparatory step for the new application architecture.
Runtime does not belong in any module, as its responsibility
is module management.

WebInspector.moduleManager becomes self.runtime.

BUG=391566
R=pfeldman, vsevik

Review URL: https://codereview.chromium.org/439293002

git-svn-id: svn://svn.chromium.org/blink/trunk@179645 bbb929c8-8fbe-4397-9dbb-9b2b20218538