fix typo
redraw phase-correlation only when changed
readme fix typos
break out common cairo functions in prep for custom button
break out pango context.
add prelight to dial widget
use custom button in goniometer

* implement custom button
* add show/hide prefs to goniometer
* change all checkboxes in goniometer
add custom radio button widget
test custom radio button in ebur128
continue previous commit (use custom buttons)
ebur128: align display area
replace spin-button with custom widget
replace spin buttons in goniometer
gtk colors & custom [in]sensitive rendering
prepare custom push button, change colors of buttons
use custom push-buttons in ebur128
last custom widget in line before GL: the fader :)
use new fader widget..
speed up metrics rendering