Add possibility to make title bar button for "Aways on top"

Submitted by Peter de Ridder

Assigned to Olivier Fourdan @olivier

Link to original bug (#2354)

Description

xfwm gives possibility for title bar buttons for stick, shade, etc. It would be nice to have it also for "Always On Top". Not everyone needs that but it's quite handy. Same counts for the shortcut keys as reported in bug 1121 (Add possibility to make shorcut for "Always on top")

Reproducible: Always Steps to Reproduce:

Version: 4.4.x