Add a new "Guide To Monitor" with walkthroughs of the new editor.

Includes guides for service checks and more, following along with the new editor that will be released in a couple weeks. I re-wrote pretty much everything from the guide to alerting so that it follows the structure of the editor a little better. I've also added many additional details on the different fields to (hopefully) help with support changes.

The page is not yet linked so we could release this without having it live.

Open questions/thoughts:

* How can I do a redirect in this repo? I want the old alerting guide to redirect to this page so we can keep the "monitor" language consistent with the app.
* Need to update the old "service checks" page to use the "network check" language. Maybe a redirect there as well?

Screenshots attached:
![screen shot 2014-09-30 at 10 44 13 am](https://cloud.githubusercontent.com/assets/472446/4460147/881332f8-48b0-11e4-93d2-5852fc78ee3f.png)
![screen shot 2014-09-30 at 10 44 25 am](https://cloud.githubusercontent.com/assets/472446/4460143/8808e55a-48b0-11e4-8af5-2c4cf5871cb9.png)
![screen shot 2014-09-30 at 10 44 32 am](https://cloud.githubusercontent.com/assets/472446/4460145/880dcbce-48b0-11e4-8123-e7906491e77d.png)
![screen shot 2014-09-30 at 10 44 47 am](https://cloud.githubusercontent.com/assets/472446/4460146/880f2bfe-48b0-11e4-92f0-13aa59f8882a.png)
![screen shot 2014-09-30 at 10 44 53 am](https://cloud.githubusercontent.com/assets/472446/4460144/880ad3ce-48b0-11e4-8554-5b627a62f468.png)





might be nice to add a link to custom check creation page.