Merge pull request #12690 from eileenmcnaughton/member_dates

Convert membership date fields to datepicker & form to entity form

diff --cc CRM/Member/Form.php
Simple merge

diff --cc CRM/Member/Form/Membership.php
Simple merge

diff --cc CRM/Member/Form/MembershipRenewal.php
Simple merge

diff --cc templates/CRM/Member/Form/Membership.tpl
Simple merge