improved front end

- moved db files to db folder
- placed all on click code into their own respective functions (to clean
up clutter)
- created a message-box that comes up to prompt user
- upon submitting login, back end sends message back to front end. front
end javascript decides what to do for each message. whether to tell user
to try again later, or that their account doesn't exist. or to just say
that they're logged in.
- after submitting log in form, javascript ajax communicates with back
end to set up session variable, to finish "logging in",