go to the start of display line
As was linked on #389 Alt+Home and Alt+Shift+Home are provided directly by the Scintilla editing widget, they are not handled by Geany which does not know about the display line.
So changes to their functions need to be addressed there or the keybinding in Scintilla could be unset at startup and the keybindings moved to Geany where they can be re-bound, but the functionality would still be what Scintilla does.
Pull requests to do that and providing options to add alternative functionality that do not remove current default functionality are welcome.