cont'd work on automation-track headers (amend ba53af1c5)

now that the separator line is at the top,
offset region-contents y0 by 1px.
revert pixfader to sane state (reverts parts of bb70d426)
proper automation header indenting
clean up rec-en circle math and limit the max radius of it
tweak button size request
add "close/cross" special button
use close/cross button