Updated gitignore

Files with "_old" in them will no longer be included in the repo.

This naming convention is being used to preserve old graphics.
Keyword Search

Keyword search now has a UI (which is shown only to administrators as
per Jason's request).
Schema Update

Updated the schema to support new payment information.

The membership dues-related fields (IDs which link payments to
membership years and types) are now nullable so that other payments may
be stored in that table.

There is now a "response" field which will be used to store the raw
credit card receipt from e-xact.
Modified Logo

logobg.png -- the logo file used for wherever the logo will be on a
white background -- has been improved.  It no longer has a blue
background, instead having a thin blue border around the characters.

This alleviates the issue of the logo blending into white backgrounds
while maintaining a sleek, professional look consistent with the colour
scheme used throughout the site.
Receipts

Fixed a bug in payment.php related to possibly incompatible types of two
variables.

receipt.php is no longer the e-xact postback page -- that function has
been moved to exact_postback.php -- it is now used to generate receipts
for payments.

E-Mail receipts for credit card payments are now generated using
receipt.php instead of using e-xact's automatically generated receipts
(which are no longer sent).

receipt.php may also be used to regenerate any receipt on demand.