move ardour meter globals into dedicated namespace (TODO meter_patters typedef)
simplify meter-type context menu

in preparation for adding more meter-types
add VU and IEC meter DSP (from jmeters)
add new meter-type enums (amend 80aa2574)
Revert new meter types (postponed until after 3.3 release)

This reverts commit ce621d1c8a600853be0020942a9664ccee0ab165.
This reverts commit 80aa2574819e947668092c660d767e25a661c6f1.
Merge branch 'apple' of https://github.com/mfisher31/ardour
add option to disable cairo-RGBA overlays for meters.
tweaks to NO_PLUGIN_STATE logic
more plugin state debugging
finally get to the bottom of where NO_PLUGIN_STATE needs to be in order to be useful