Issue Summary

Same as title.

Steps to Reproduce

1. Sign in as an admin.
2. Go to the "Site logo and favicon" settings page.
3. Upload a logo.
4. Click on the "undo" link after the colour scheme info appears.

Expected Results

Should be able to undo the updated colour scheme.

Actual Results

Method now allowed page appears and 405 thrown.

Workaround

If the previous colour scheme was the default one, the user can go to the colour scheme page, edit, the reset. If the colour scheme was a custom one, that changes will be lost.