create behat step to use relative dates in forms

[Rebecca Blundell]

Currently it is only possible to add specific dates to forms, e.g. in Shared_views_to_group.feature. This means that adding a date in the future is unreliable. I want to add a step like:
And I fill in "css element" with "relative date" date so that steps like:
And I fill in "accesslist[0][stopdate]" with "next month" date
are possible.

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/7962

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/7962
Committed: https://git.mahara.org/mahara/mahara/commit/2ca67cfb0bbb68c62ea591f8e523410bb16efb2e
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit 2ca67cfb0bbb68c62ea591f8e523410bb16efb2e
Author: Rebecca Blundell <email address hidden>
Date: Thu Aug 31 15:34:53 2017 +1200

Bug 1714143: Add step for filling in a relative date.

Adjusted the plan/task test to use new step

behatnotneeded

Change-Id: Ieded116f26f73690a1cbde2c6d2de63828e1092f