Update dpm top bar to use agreed branding

- New image and spacing to make it work
- Use logo formatted name without adding line breaks on eo pages

https://www.pivotaltracker.com/story/show/48560501
Custom top bar colours for EO pages

Enable the possibility of having a custom top bar colour. Currently this
is only going to be turned on for the EO offices while we think about
which colours to use for other departments.

https://www.pivotaltracker.com/story/show/48560651
Merge pull request #477 from alphagov/eo-top-bars

EO top bar branding

https://www.pivotaltracker.com/story/show/48560501
https://www.pivotaltracker.com/story/show/48560651