Merge pull request #4 from atlet/master

Calendar integration
feature: send mail to booker instead to booked added
install.xml missing next previous for moodle 2.4 added
moved sendmailtobooker to appropriate section on booking settings
typos in language file corrected
fixed wrong link formatting in plain text message
added validation of username for bookingmanager
new release version.php updated
Merged from github user atlet
added previous/next attributes for moodle 2.5 compatibility
resolved upgrade problems
bookingmanager help string corrected
language strings fixed
Table has full width.
Showing search users...
Updated cron
Added help.
user selector search now possible
english spelling mistake fixed: poolurl to pollurl
German language strings updated