Show current or former position in MP page header

A combined fix for #449 (current position) and #528 (former position), building on the layout work done in #553.

The extra paragraph only appears if the template is passed a `$current_position` or `$former_position`. If both are supplied, the `$current_position` is preferred.

This needs some developer attention to actually populate `$current_position` and `$former_position` with the right values.

![silly-walks](https://cloud.githubusercontent.com/assets/739624/3412962/39a8c7bc-fe06-11e3-9668-8c161f9ef5ab.png)

![former-pm](https://cloud.githubusercontent.com/assets/739624/3412963/39a8d298-fe06-11e3-8ba2-30ae8a174418.png)

![queen](https://cloud.githubusercontent.com/assets/739624/3412964/39a94ffc-fe06-11e3-92e4-d5f2929e98ea.png)