fix another peak-meter threshold config issue
fix rendering of meter metrics w/o types

For example the initial meter widget in  the file-import dialog.
improve timing accuracy for meter-falloff calc.
meterbridge: ignore non-visible routes/meters.
experimental RMS-meter and peak-signal (vs peak-power) query
amend to 1ada5330b

fix deadlock when updating audio/midi connection matrix
during session-close or on exit.

(Note: this still can cause a crash if the route goes away
while the iterator in the connection-matrix still has an index
of it)
don't reset meter background/highlight on click.
amend to af041c0d and 1ada5330b - fix port connection matrix crash on close
fix metering when monitoring track input. (ran twice)
possible fix for crash on exit - err on the side of caution
fix/workaround window-proxy session-management

The window proxy defers construction of classes.
set_session() is called before the instances are available.
the proxy-manager only calls set_session() for SessionHandlePtr
but not the class-specific method..

fixes http://tracker.ardour.org/view.php?id=5566
Merge branch 'master' into meterbridge

Conflicts:
	gtk2_ardour/ardour_ui_dialogs.cc