Xpad - autostart options

This specification describes the functionality of autostarting Xpad by the preference menu.

In the preference menu a checkbox is added called "Start Xpad automatically".
In the preference menu there are the following sub checkboxes of "Start Xpad automatically"
- Open all pads / hide all pads
- Start a new pad

If the checkbox "Start Xpad automatically" is activated, then the subcheckboxes become available.

On the technical side, different implementations have to be taken into account for the following desktop managers (Unity, Unity2D, GNOME, LXDE, XFCE, Kubuntu).

Another technical note is that the start of Xpad needs to be delayed when all the pads need to be hidden, since the panel is likely not to be started when Xpad is already started, resulting in the autohide function not working.

For Unity, Unity2D, GNOME this method can be used in the xpad.desktop file:
X-GNOME-Autostart-Delay:10

For LXDE, XFCE, Kubuntu this method can be used in the xpad.desktop file:
Exec=bash -c "sleep 10 && xpad -h"

On some DE's the autostart needs the dependency of the systray to be able to hide the pads on startup.

For LXQt add this to the xpad.desktop file:
X-LXQt-Need-Tray=true

Work items:
Add the "Startup options" preference label: DONE
Add the "Start Xpad on login" preference checkbox: DONE
Add the "Wait for systray" preference checkbox: DONE
Add the "Start a new pad" preference checkbox: DONE
Add the "Open all pads / hide all pads / Restore previous state" preference radio button: DONE
Add the dependency for the the three last options on the first option (grey out): DONE
Implement the "Start Xpad on login" preference: DONE
Implement the "Wait for systray" preference: DONE
Implement the "Start a new pad" preference: DONE
Implement the "Open all pads / hide all pads / Restore previous state" preference: DONE
Implement the "Delay startup" preference: DONE