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When an event was moved both to another day and also time of day three
HTTP requests were fired by the websocket support:

1. PUT event under new date, but with still old time of day
2. DELETE event
3. PUT event with new time of day

This obviously lead to the problem where subsequent event updates such
as request 3 failed with HTTP 404 Not Found. So, operations 1 and 2 need
to be changed, the event needs to be first removed before it is added to
solve this:

1. DELETE event
2. PUT event under new date but with still old time of day
3. PUT event with new time of day

However, another problem manifested right away. Reqest 3 always overtook
request 2, resulting in an HTTP 400 Bad Request for the earlier arriving
partial update request, as the expected new event is not complete. The
last arriving new event request succeeded, so one would think that
eventually things automatically healed themselves. However the event
still contained the old time of day, thus the shown event information
were in fact wrong.

I've no idea why requests didn't arrive in sending order. I verified
that they are queued for sending in the correct order. I can only
imagine that the partial update is quite a bit shorter than the new
event request and this somehow leads to a race either on the wire or in
the network access manager itself. Whatever. The network access manager
can send up to six requests in parallel, however there's no builtin
mechanism to change this:

> Note: QNetworkAccessManager queues the requests it receives. The
> number of requests executed in parallel is dependent on the protocol.
> Currently, for the HTTP protocol on desktop platforms, 6 requests are
> executed in parallel for one host/port combination.

– https://doc.qt.io/archives/qt-4.8/qnetworkaccessmanager.html#details

See the code comments for details on this change.

The next commit will introduce new typed signals, but the classes are in
the wrong order for this dependency change. Move `TimeOfDay`, `Event`,
`Service` and `Action` before `Day`, so that at time of `Day` class
definition evaluation the `Event` class is already known. `Event` relies
on `TimeOfDay`, that's why this has to be reloacted, too. Both derived
`Service` and `Action` classes are moved as well to keep all event
related things together.

This makes things only much more complicated when generating new IDs for
new events. This will generate even shorter IDs and as we're having a
counter anyways, we're not producing duplicates.

The `QNetworkAccessManager.deleteResource` only accepts a
`QNetworkRequest` object but no body buffer.

Previously the `ResponseHandler` object was deleted before it had a
chance to get called. When the method ended the objected was destroyed,
now we avoid that by adding it into a set and removing it afterwards.

* widen table to use available space, top and bottom page margins are
  reduced to one centimeter, too in order to match left and right
  margins

* reduce table header to only a single row, the date from the line below
  is now moved up into the same as the weekday

Sometimes the operator wants to create an action but instead he creates
a service or vice versa. This can be kept unnoticed for quite some time.
Previously one had to either change the JSON manually or remove the
event and recreate it by hand with the correct event type – hopefully.

This commits adds the possibility to morph events into the other event
type directly. It is available in both the context menu and main menu.

Also add the translations.

When both Manu W. and Manu T. are the people mainly responsible for an
action I just want to write „HV: Manu²“ but this broke the LaTeX export.

The description is now placed with a single line break below the
assigned custodians of the event. The complete extra row is removed, so
even more space is saved in the PDFs.