Better error handling for Stripe checkouts.

[andrewlimaza]

Describe the bug We should improve the wording on error handling that Stripe returns. In some cases, we post the exact response we receive from Stripe and this may be confusing to the end user.

To Reproduce Steps to reproduce the behavior:

1. Make sure you have Stripe enabled, and require billing address.
2. Fill out all details except first name and last name under the Billing Address section.
3. Scroll down and select the checkout button.
4. See the error above the checkout button. (Please refer to screenshot below).

Screenshots

Expected behavior The wording can be improved.

Isolating the problem (mark completed items with an [x]):

• [x] I have deactivated other plugins and confirmed this bug occurs when only Paid Memberships Pro plugin is active.
• [x] This bug happens with a default WordPress theme active, or Memberlite.
• [x] I can reproduce this bug consistently using the steps above.

WordPress Environment

``` Please share non-sensitive information about your hosting environment such as WordPress version, PHP version, Paid Memberships Pro and any related plugins versions. ```

[kimwhite]

Is this being looked at doing at some time?