Tweaks plain button style and more subsection conversion

1. Brings plain button style more in-line with 8shapes mockups.

Before:
![](https://s3.amazonaws.com/uploads.hipchat.com/18157/80205/U2t0JknmzrxCD1V/Repositories_-_Sonatype_Nexus.png)

After:
![screen shot 2014-10-27 at 10 27 48 am](https://cloud.githubusercontent.com/assets/186715/4795773/2f33245e-5dff-11e4-8a2b-6e60bc27b99b.png)

2. Converts health check nested form to a subsection

Before:
![](https://s3.amazonaws.com/uploads.hipchat.com/18157/80205/8dEPCI5qlQIa2i5/Repositories_-_Sonatype_Nexus.png)

After:
![screen shot 2014-10-27 at 10 26 56 am](https://cloud.githubusercontent.com/assets/186715/4795774/336b62b6-5dff-11e4-82c6-1e782bc66f6f.png)