Add column 'latex_template' to ProtocolType to use in the compiling process and the corresponding view

#170

/close #173

ref #173

#165

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

/close #155

/close #141

/close #93

I.e. do not delete orphan todos if the protocol names them by ID.
That happens if the todo is created using the web interface.

/close #105

ref #94

/close #53

/close #87

/close #108

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

/close #45

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 #80

/close #71

/close #64

/close #63

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

Allow to optionally use non-reproducible random uuids as etherpad links (#45)

/close #32