fix input metering:

if meter==input, meter depends on In/Disk
see also 29108187ed
fix "monitor mode 11"

see http://www.oofus.co.uk/ardour/Ardour3MonitorModesV2.pdf
the overall logic can probably be simplified somewhat
track-rec-enable on -> always monitor input
RMS meter - reset after calculating new data
increase spacing between meter ticks and labels
move ff* structs & typedef into dedicated namespace

(further avoid conflicts with plugins)
zero meters for inactive tracks
fix metering states 34, 38, 49, 50, 53 and 54

for state descriptions see
http://www.oofus.co.uk/ardour/Ardour3MonitorModesV3.pdf
Merge branch 'clang' of https://github.com/axetota/ardour
yet another meter+monitoring detail:

"explicit Monitor DISK" + "Transport Stop" + "not track rec-en"
 -> meter is always zero
Revert "C++11 Building - Use new style struct field inititializing" (this code
change breaks gcc on several platforms).

This reverts commit bf153e58a5e3b31536648bff4b95bf6e0a107c6c.
revert functionality of f842e8af2 (meter display in DISK mode)