Membership Form -- Username to E-Mail

Membership application form no longer uses/collects/etc. username
information, relying completely on e-mail addresses.

Also, e-mails are now properly lowercased before being checked/inserted.
Edit/Add Person -- E-Mail Comparison Fix

The edit/add person form now properly lowercases e-mail addresses before
insertion/comparison.
Edit/Add Organization -- E-Mail Lowercasing

The controller which handles editing/adding organizations now properly
lowercases e-mails before insertion.

This wasn't a bug per se, since those e-mail addresses have no
constraints -- such as uniqueness -- enforced on them, and was purely a
cosmetic/consistency change.
Membership Application Beautification

Broke the membership application form out into heading-delimited
categories.
Notification Width Fix

Fixed the width of the "[y]ou may pay [...]" notification which shows up
when a superuser/admin from an organization which may pay dues is logged
in.

Was erroneously 972px due to border and padding.

Is now correctly 960px.
Schema Update -- Subtotal/Total

`subtotal` and `total` in the `payment` table are not nullable and
DEFAULT NULL.

Considering these fields for removal as they're not used/populated.
Add/Edit Payment

Added the ability to add and edit payments (administrators only).
Add/Edit Payment Links

On the organization page, superusers of that organization will be able
to click on each payment (which is paid) to go to the receipt for that
payment.

Administrators, however, will be able to click any payment to be taken
to the edit payment page for that payment (from which they can click
through to view the receipt if the payment is flagged as having been
paid).