mirror: "all" - all axis lines and ticks are mirrored

[DaanyWaay]

Ticks should be mirrored only if "allticks" is selected.
https://codepen.io/pen/ZEzpYWY

[etpinard]

essential the bug part of #2539 - thanks very much for posting!

[thchr]

I noted this over in #4140 but realized it might make more sense to note it in this issue instead:

This seems to still be be broken on v2.2.1: https://codepen.io/thchr/pen/eYWGjQM
I.e., the tick marks are on both y-axes of the first subplot.