WL-3110 Extend Utilities to support boolean configs

Currently you extract a string value and comparing it to `"true"` is a bit
combersome. Since boolean configs are super common, I'm extending the
utility to accommodate them.
WL-3110 Add server config for attendee emails

Currently an attendee doesn't receive an email if an event isn't set out
to send out notifications for all events. Arguably an attendee should get
an email when they get signed up, but it is a bit spammy to send out emails
everytime an event is modified.

As such we are introducing a new config variable for `sakai.properties`:

    signup.email.notification.attendee.signed.up

The default behaviour is, "yes do it please".
Merge pull request #15 from ox-it/WL-3110

WL-3110 Send attendees signup notifications