Better signposting of form sections that users can't see

Before this change, users couldn't even see the sections of the
form that they didn't have access to, and hence weren't even
aware that they existed. This change should aid discoverability,
hopefully leading to more users requesting appropriate permissions
for themselves.

Landing page before:

![image](https://cloud.githubusercontent.com/assets/23801/3153564/21ae0798-ea9d-11e3-823e-70211534e676.png)

Landing page after:

![image](https://cloud.githubusercontent.com/assets/23801/3153557/126c2c42-ea9d-11e3-857b-be92d9152d13.png)

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New request dropdown before:

![image](https://cloud.githubusercontent.com/assets/23801/3153572/3272b5ec-ea9d-11e3-8c24-5e8181271e9a.png)

New request dropdown after:

![image](https://cloud.githubusercontent.com/assets/23801/3153579/408dff9c-ea9d-11e3-9e66-bc5e7cd64ebe.png)

----

Forbidden page before:

![image](https://cloud.githubusercontent.com/assets/23801/3153594/669c5a76-ea9d-11e3-88aa-52c03c3749c5.png)

Forbidden page after:

![image](https://cloud.githubusercontent.com/assets/23801/3153598/6e1228f8-ea9d-11e3-8733-200be4d4a1c4.png)