Move current and former offices held code to the Member/Office classes.
Add full list of currently held offices to member pages.
Alter behaviour of current and former title positions to be more robust.
Modify current positions to only override the default if positions are
flagged as priority.
Rework parts of office listing to clarify the intent.
Better document the Office class, and reformat pretty_dates to be more readable.
Add explanation of the significance of dates, and a todo to update.
Change behaviour of "details" link on MP page policies.

Ensures the button works on touch devices.
Merge branch 'fix-policy-details-button'
Merge branch '449-current-position'