⌂ Repeat-bar-lines with angle-wings for whole StaffGroup (automatic and semi-automatic)

The here-defined CertainBracketTipsBarLines automatically adds angle wings to certain bar lines of an entire StaffGroup, relying on the new-defined property tip. To activate it, say

\override Staff.BarLine.tip = #'auto

Using values up and down instead of auto, the settings can be made explicit, offering the possibility to limit those angle wings to certain StaffGroups among others of the same score. An example for this is commented in the code below.

CertainBracketTipsBarLines is currently limited to the default repeat bars, i.e., ":..:", ":|.", ".|:-|" ".|:"