Work on "transactions" (purchases, entries)

Replace `Member#buy_membership` and similar methods in `Member`, `Guest`, and `Person` with simpler ones.  Do not save anything to the database inside these methods.
Partially fix RegisterController
Fix a small bug in inline CSS style
Fix a localization key ('admin')
Clean up
Format
Small fix in SimpleFilter

Do not upcase search string, the `LIKE` operator is case insensitive for ASCII and case sensitive for other letters.
Make User more aware of its roles
Log in users with a single role each time
Make Person declare its associated roles

Make Person declare its associated roles (member, instructor). The new method can be called to see if it is safe to delete a person.
Deal with NULL people.name_title DB values
Work on instructors and members controllers

Work on #create, #update, and #destroy actions in MembersController and InstructorsController.