Create And Update Guides

A working version of creating and updating guides. 

### What's Changed
* A lot. 
* A create guide flow that makes sense. Asks for location, overview, name of guide, and crop. 
* Users can create a crop if their crop isn't found.
* Impressions for guides and crops.
* An edit page that makes sense. Users can choose requirements and stages.
* API endpoints to create, update, and show requirements and stages.
* An API endpoint to show various stage and requirement options.
* stage and requirement options according to the design in Drive. 
* *note*: to be able to use the stage and requirement functionality, you'll have to create some mock Requirement Option and Stage Option objects in your database. 

**Requirements:**
![screenshot 2014-09-27 17 48 51](https://cloud.githubusercontent.com/assets/485583/4430502/ed9007a2-4633-11e4-9dc5-4d92fb9e77ad.png)
**Stages:**
![screenshot 2014-09-27 17 49 42](https://cloud.githubusercontent.com/assets/485583/4430505/070af5fc-4634-11e4-9c48-d620040568dd.png)


### What's next
* User testing on the create and edit guide flow.
* Weighted search results. We should take some time to weight crops we think should come first "Twisted thistlebear" shouldn't be it. 
* Tweaking to stages on the guide edit stage.
* Image uploading for guides (@rickcarlino, I need to talk to you about AWS keys and such)
* Editing the actual guide page to be in line with the edit guide page.
* Some more complete tests

So much to do! I will tag the things that this closes at a later point. For now, I'm anticipating the hound. 
Also: typically delete actions will `render nothing: true` rather than return empty JSON.