Repeated Date Formatting and Missing reminder_date in renewMembership

This patch removes the customFormat calls in renewMembership on membership dates coming from getRenewalDatesForMembershipType as getRenewalDatesForMembershipType was already returning dates in the same format as customFormat was generating.

As well, $memParams['reminder_date'] is now set at the same time as the end_date when handling current memberships. Prior to this being set (using annual memberships as an example):
1. A typical member would receive the reminder email as their first year of membership ends.
2. Having sent out the email, UpdateMembershipRecord.php sets their reminder_date to NULL.
3. Someone renews the membership before the end of the grace period for the initial / first year of membership.
4. Only end_date is adjusted to reflect the renewal.
5. Because reminder_date was never changed after step 2, no reminder email is sent to the member as their second year of membership ends.

The patch was generated against 3.0.4, but should also apply to 3.1. The reminder date issue seems to be present in (at least) 3.0.2, 3.0.4, and 3.1 beta 6.