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.
Add paragraph to person pages explaining where we source vote data.

Closes #504
Update build status images and add installability badge for consistency.
Add mailing address to automated alert mailings.

Closes #640

As per discussion on #640, add our physical mailing address to automated
outgoing alert emails (ie those which just happen, and are not explicitly
initiated by a user).
Don't log anything with 'both' in the useragent.
Merge branch '640-emails-postal-address'
Merge branch '504-data-sources'
Merge branch 'fix-policy-details-button'
Merge branch '449-current-position'
Update Member->image() to return an array of useful data, instead of
just the URL of the image.
Update person pages to use new arrayed image data; reinstate the message
about providing images where we have none.

Closes #443
Remove now-unused person_image function