Here's what I did:
- Took out redundant getters and modified tests to expect ints
- Standardized on 'expiration' instead of 'expiry'
- Reverted to former FORM width, tweaking only expiration field
- Stuck with pixels for FORM layout (a switch to em should be done as a
whole, and #66 surely affects this)
- Show expiration error before CVV to match order in UI