#16 edit the templates from the web admin interface

[Konrad Wulf]

It should be possible to edit all the templates
(badges, invoice, mails) and preview them from the web
admin interface, as the contents usually comes from the
conference chair / organizer who is not necessarily the
sysadmin and may change over the phases of the
conference...

It may even be useful to edit some parameters of the
central configuration in the web.xml there ...