Add ability to search for amounts on "Registrations" page

[monicabritton]

This is a replacement for issue #133 . Please add a field at the top of the Amount column (like there is for other columns), allowing the user to search for all registrations with a specific payment amount. (Thanks!)

[amschaal]

Added on both registration search page and manage event registration table. Must be an exact match for the original amount paid.