Context stack lines is not sent back to GUI on startup

[AlEscher]

If the user sets pwndbg's context-stack-lines in his .gdbinit file, the stack lines spin box in the GUI is not updated to reflect this.
This was implemented previously, however it resulted in endless recursion if the user clicks on the spin box incrementors in rapid succession. Qt would keep endlessly firing different signals forever.
A better way of sending updates from GDB back to the GUI on startup should be found.
This only affects the stack lines counter atm.