Added and used checkMailNotInUse method
fixed changelog
removed extra blank lines
check mail also in edit user form
undo bad typos
check also couriermailias to see if a address is not in use
better error for checkMailNotInUse
better mail in use error message for alias
remove mailbox-related objectclass and its uses
added documentation for checkMailNotInUse
Merge branch 'master' into groups-check-mail

Conflicts:
	main/mail/src/EBox/Mail.pm
	main/mail/src/EBox/MailAliasLdap.pm
	main/users/ChangeLog
	main/users/src/EBox/Users.pm
removed extra blank lines
Merge branch 'jag/groups-check-mail'