Schedule or Send Mailing - Send Immediately checkbox should be unchecked if user selects a date in Schedule Mailing calendar pop-up

Currently, when Schedule or Send form (step 5 of mailing wizard) loads, the "Send Immediately" box is checked. If the user picks a Scheduled Date from the calendar, "Send Immediately" is still checked AND when the form is submitted the Scheduled Date is ignored. The mailing is scheduled for now(). This is quite confusing and problematic since there's no way to change the scheduled date.

Add jQuery logic to "uncheck" Send Immediately ("now" field) if user picks a date from the calendar pop-up (start_date).