error icon for main-toolbar

This is something I've made out of need when working with Brackets especially on non-brackets projects (when I don't have my Brackets developer console open) to see if something wrong happened inside Brackets immediately.

From my experience many users don't use console to look for errors before reporting an issue so having a red icon appearing on the main toolbar might help also to non-developers.

Leaving to your consideration if this's a good idea for a default extension, or if I should move it to the extension registry. I'm fine with both.

Looks like this:
![image](https://cloud.githubusercontent.com/assets/1067319/2797497/a9432c9c-cc2f-11e3-8ab5-d241bddb7b77.png)