add lib/LV2 path akin to lib/surfaces, to allow bundling of LV2 plugins in an ardour release.  My first attempt to push...
basic window infrastructure for meterbridge
implement meterbridge & meter-strip
meter-bridge details:

* sort routes
* draw metric area
* layout & style
meterbridge: fix initial and max window size.
set window title of meterbridge window
allow to set level-meter min width
overhaul meterbridge:

* rotate labels, fix size
* identical total width for mono + stereo meters
* show metric area only every 8th meter
* ...
session property - include busses in meterbridge
meterbridge: add rec-enable btn & prepare metric/tick separation
meterbridge ticks/metric experiments..
add peak-hold button (independent from mixer)
disable all meterbridge metrics & ticks for now
fix meterbridge window behaviour on session unload/close.
fastmeter: 1px padding left&right
meterbridge: honor DPI, Color & Theme changes
meterbridge label alignment & height
add margin around meters in editor track header
adjust padding of meters in time-axis view (still using border bg color)
meter background gradient (hardcoded colors so far)

this is a quick test w/black borders only left+right
for Mr oofus to assess.