Update guides according to wireframes

### What's new

* A new "Create Guide" page. 
* Sensible Ajax alerts (though still not pretty, nor DRY)
* Various styling updates
* Better guide styles
* Updated API crops search, and fetch specific crop, tests
* New API for guide, simple tests
* Update to Edit Guide page, which is visually a step backwards, but technically a step forward. 

### TODO
* More tests on guide and crop API controllers.
* Start seriously implementing edit-guides functionality.