BUG: The option to have daily subscription renewals needs to be disabled

[JarrydLong]

CCBill doesn't seem to support this interval

[ideadude]

A work around is to do one time payments that expire in 1 day or X hours (when granular expirations is launched for PMPro core).

[ideadude]

We should warn people if they set up a level that renews every day.

There is no filter to remove billing periods from the dropdowns. Our solution is to add a function to check levels for compatibility and throw errors in the admin.

Here's the code in the PayFast gateway that does this: https://github.com/strangerstudios/pmpro-payfast/blob/dev/pmpro-payfast.php#L59-L89

[ideadude]

Let's also detect if a "Custom Trial" is used and show an error for that.

You CAN have an initial payment different from the recurring amount, but you can't have tiered "custom" trials.