Automatically hide poll and set expiry date

[surfdemon]

As an administrator I can set an expiry date for a poll so that it automatically hides when the poll ends

[surfdemon]

Acceptance Criteria

• The admin section for the polls should have a date field to set the end date of a poll.
• When the date gets to the poll end date the poll should no longer show on the website

[surfdemon]

** Tasks **

• Add date field to poll
• Update Poll so that it no longer shows on website when end date is reached (if there is an end date set)