GUI for custom screenlocker on x11

[stefonarch]

Needs https://github.com/lxqt/liblxqt/pull/346

Settings go to session.conf which is more natural as also the delay is here and it is about session locking. The PR above checks for backward compatibility first lxqt.conf.

[General]
__userfile__=true
leave_confirmation=false
lock_command=slock
lock_screen_before_power_actions=true
power_actions_after_lock_delay=2250
window_manager=kwin_x11

We could also remove the "custom" and use xdg-screensaver lock as empty/default value.

In the list I added all screenlockers from here, except AUR.

Window Manager → X11 Window Manager

[stefonarch]

With some help from @tsujan done.

[luis-pereira]

Testing it

[stefonarch]

@luis-pereira Updates?

[stefonarch]

There can arise a situation when the user has xscreensaver enabled in autostart, enabled screenlocking in it and uses also a custom screenlocker:

• clicking "lock screen" the custom one is executed
• when "lock screen before suspend" is checked xscreensaver's lockscreen appears at awake and after unlocking the message "could not execute slock, make sure it's installed etc" is shown.

Maybe we could add a tooltip "Make sure no xdg-screensaver compatible screensaver like xscreensaver is running at the same time" or similar.