ctrl-click when adding automation points no longer adds guard points
Revert "add a hack to deal with device discovery race, in which the devices were not actually known to be ready before the last update_surfaces() call (which is where binding between strips and routes occurs) ; add support for Mackie Control touch on/off messages"

This reverts commit 06a25ffd5695697db9869a19e46c2f93c6c17458.
click (no drag) on automation line now adds a new control point on the line (not fully checked for precision)
fix prev_snap_choice() key="3" binding
the forgotten second (amend to prev commit)
reverse default behaviour for adding control points to automation with mouse clicks. unmodified click adds new control point without guard points; ctrl-click adds new point with a guard point (old behaviour)
tweak canvas rect drawing to correctly place bottom edge of rectangle inside the bounds (cairo works in mysterious ways)
fiddle with single pixel adjustments to time axis view item heights; fix region gain envelope visibility
reorder (in source only) positioning of ruler/marker canvas groups
indent/align