Better defaults for .primary + .secondary contexts

When `editor_for_symphony` is enabled and a `textarea` field is in the sidebar, the default height of 450px is long. Like really, really long:

![screen shot 2014-08-01 at 2 03 53 pm](https://cloud.githubusercontent.com/assets/275617/3785122/ce6f4630-19bf-11e4-8c46-c317ad91e5ef.png)

This makes it better suited in the sidebar context while still giving proper treatment in the `.primary` column:

![screen shot 2014-08-01 at 2 04 11 pm](https://cloud.githubusercontent.com/assets/275617/3785125/d8475a4e-19bf-11e4-84d7-8ec6a0e34e9a.png)