This adds default values to default metadata and the option to set it
before compiling the protocol (i.e. while planning to TO).
Additionally, the (dynamic) metadata fields are handled correctly in the
ProtocolForm and metadata is shown while still planning.
Additionally, protocol.start_time is used instead of
protocoltype.usual_time.

/close #47
/close #65
/close #106

Enable using multiple authentication backends.
(Samba-)AD and LDAP-Backends are implemented.
Session timeouts are implemented.

/close #17

/close #21

/close #86

If there are todos which have todo.who == current_user.username, show
only them, as there may be quite a lot of open todos in total.

/close #90

e.g. [todo:who:what]
e.g. [todo;who]

/close #95

/close #98

Create LocalTOPs when creating Protocols or DefaultTOPs, not on demand
when necessary, since that created double entries.

reference #96

/close #81

/close #77

/close #74

/close #71

/close #64

Categories can be set per protocoltype.
They are specified as another semicolon-separated argument to
[beschluss;…].
Decisions can be search for their category.
/close #53

/close #54

/close #57

/close #52

If the protocol is not on the same day, show a warning before pushing
the template to the etherpad. #44

/close #50

/close #39

/close #36
/close #28