make session creation from a template work again
use WindowManager/WMProxy to correctly manage the audio/MIDI setup window
the output of git describe --tags is not subject to localization, so we do not need LANG= in the environment when it runs
major rearrangement of startup/session loading code

first-time user code remains in ArdourStartup
session selection/setup moved to SessionDialog
many other cleanups, logic improvements, and so forth to the overall session loading process.
Not 100% finished yet.
move announcements frame around in the session dialog and adjust spacing/borders
move rate_as_string() from EngineControl to utils.cc
add new static functions to get SR and disk sample format from session XML
use new Session API to show session SR and disk bit depth in recent sessions list
shrink small-splash.png image by 50%
tighten up layout of session dialog; make button say cancel or quit in difference scenarios
fix crash when cmdline provides session name
start explicitly linking against libtimecode (this needs to happen elsewhere too)
make information extraction from session file options list robust against some old badly formatted session files

Fixes crash experienced by GillesM, where a rogue XML entry caused a segfault
fix up enum mess caused by switching from JACK to Engine as the name for jack-related transport sync

This will allow older versions of Ardour to continue to startup when the user sync preference is "JACK",
because the string used by enum_2_string() will still be "JACK".

Versions of ardour3 from git after the enum change until this commit will leave ardour.rc unloaded by old
versions of Ardour ***if*** the user sync choice was "JACK".
don't ping JACK server 4 times to see if it is already up when ardour starts
fix up crash caused by changes in object creation order and setting the state of the click IO object
Add AudioBackendThread class to support different thread type on windows
Move processing thread list from ARDOUR::Graph into AudioBackend implementation
Implement JACKAudioBackend::in_process_thread
remove OSC related cruft from ardour_ui_options.cc

control surface activation is handled via an entirely separate mechanism now