Parse dates for volume graph as DD/MM/YYYY

@moonpxi
@gtrogers
Add fixture for LPA volumes

@moonpxi, @gtrogers
Feature test fixtures override existing stub config.

@gtrogers, @moonpxi
Change conversion funnel to use Mon -> Sun weeks

@moonpxi
@gtrogers
Revert "Change conversion funnel to use Mon -> Sun weeks"

Pushed commit to wrong branch -_-

This reverts commit 667d1d6168c5e827629d4b0b4ffd4bfc2ec60ead.
Merge pull request #123 from alphagov/change_date_parsing

Reasonably sure that this is failing because of flaky feature tests. Experimenting with the time out in another branch so merging this one now.