Also fixes some latent bugs

More or less directly taken from http://flask.pocoo.org/snippets/120/

/close #175

/close #173

ref #173

ref #173

/close #161

/close #119

This adds the configuration key MAX_PAST_INDEX_DAYS_BEFORE_REMINDER
ref #158

This adds the new config key MAX_PAST_INDEX_DAYS
ref #158

This creates a new protocol of the current type on the given date and
optional time.

/close #155

ref #116

/close #116

/close #132
/close #130

/close #117

/close #93

/close #114

ref #94

/close #53

This enables to generate both AStA-style and FS-style (and in theory
other) protocols.
/close #88

/close #104

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