This commit adds a new tab to the Settings modal: Debugging
This new tab has the append component stacks feature and a new one: break on warn
This new feature adds a debugger statement into the console override
Update various parts of DevTools to account for the fact that the global "hook" might be undefined if DevTools didn't inject it (due to the page's `contentType`) it (due to the page's `contentType`)
Sebastian Silbermann
Brian Vaughn
Mark Huang