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.
Don't set the Cache-Control header on dev sites

Varnish observes the Cache-Control headers on our development server,
which is frustrating when you're actively changing the source and can't
see the changes when you reload the page.

This commit makes sure that TheyWorkForYou only emits Cache-Control
headers when DEVSITE is falsy.
Make configuration example aware of already defined constants.

Reduces the barrage of warnings during testing.
Update Composer and dependencies.
Merge branch 'reduce-test-noise'
Merge remote-tracking branch 'origin/no-cache-control-for-devsites'
New policy position on shares for rights

Closes #573
New policy position on local government powers

Closes #574
New policy position on secret courts

Closes #575
New policy position on communications data retention

Closes #621
New policy position on a register of lobbyists

Closes #622
New policy position on fees for lawyers in no-win no-fee cases

Closes #623
New policy position on letting agents' fees

Closes #624