Add option to run command before UI is initialised (closes #798)

Signed-off-by: AnErrupTion <anerruption@disroot.org>

res/config.ini

@@ -312,6 +312,10 @@ sleep_cmd = null
 # Specifies the key used for sleep (F1-F12)
 sleep_key = F3
 
+# Command executed when starting Ly (before the TTY is taken control of)
+# If null, no command will be executed
+start_cmd = null
+
 # Center the session name.
 text_in_center = false