FLARM/Declare: Replaced declared turnpoint name with number

The number of turnpoints in a task declarations depends on the number of
characters in the turnpoint names. By making the names as short as possible
we can squeeze out a few more turnpoints.
ObservationZoneClient: use nullptr instead of NULL
test/FaultInjectionPort: remove fake Port symbols

Just link TestDriver with the original Port.cpp.  After a few rounds
of refactoring a while ago, this is possible.
NEWS: prepare for 6.7.6
Device/Port: remove the "receive timeout" from API docs

The "receive timeout" has been obsoleted by the new method WaitRead().
Device/Port: move code to WaitAndRead()

Eliminate duplicate (and fragile) driver code.  Making the return
value unsigned (i.e. size_t), the API is somewhat more robust.
Device/Port: add a more complex FullRead() overload
Driver/LX: relax download timeout

Allow a memory section download to take up to 5 minutes.  The old
timeout was just one minute, which was not enough for long flights on
4800 baud.
Merge branch 'v6.7.x'
Device/Simulator: don't generate FLARM traffic

According to the code comment, this was used to test the FLARM NMEA
parser.  That's not necessary anymore, because we have unit tests for
that.  Anybody who wishes to simulate FLARM traffic shall use NMEA
replay.
Device/Config: remove option "Ignore checksum"

This option is dangerous, but desperate users always enable the
option, hoping it will help with their problems, but it will not.
Let's just drop support for devices that are so broken they can't even
generate correct (mandatory) checksums.