adjust LV2 ringbuffer size according to LV2:resize-port

The message-size itself is part of the message which
stored in the ringbuffer. If the rinbuffer overflows
the message is misinterpreted -> segfault.

Choose a more conservative ring-buffer size and take
the requested LV2 size into account.
fix logic for display of transport bar meters

Always remove from parent (if there is one), then repack if necessary.
xmas-egg
fix reasonable synth octave
remove some unused code from mackie support
Mackie Control support now saves & restores port connections for devices not using ipMIDI (not required for ipMIDI anyway)
make MIDI UI in libardour handle CallSlot requests like it used to (and like it should)
change Generic MIDI control so that it handles a SendFeedback request synchronously within a process callback
rsynth.lv2: fix note off+on follow up:

special case if the same note is turned off and on in the
same [internal] synth cycle (64samples). x-fade to ADSR attack.
fix a crash caused by not checking if MackieControlProtocol::_surfaces_state exists

I forgot to add this check when i changed the member variable to a pointer.
mnemonic PDF: margin, URL, and (C)year updates
midi clock slave: make bandwidth variable according to period size
midi_clock_slave.cc: Better debug messages
midi_clock_slave: fix wrong calculation of loop error

since transport_frame refers to cycle start, the should be position has
to account for position of the midi clock event.
interpolation_test: add some necessary assertions
midi_clock_slave: fix bandwidth to 2/60 for best results
longer text description
new ControlProtocolManager API, and proper handling of view/model changes in the RC options (prefs) editor
clean up aspects of ControlProtocol API
clean up aspects of ControlProtocol API