Automatic secondary display selection

To make the initial setup easier, OpenLP could
automatically always use the secondary monitor
as default, if available instead of using the
primary monitor.

Additionally OpenLP should switch the display monitor to 2nd
monitor if it is plugged in during the usage.

There could also be a checkbox "Use primary monitor to display Live",
for switching to main display/checked if only one monitor is used.

In case of 3 or more monitors the user could select from the additional monitors.

Some users have reported having problems with the
display setup, for example see:
https://forums.openlp.org/discussion/3624/monitor-display-for-a-labtop#latest
https://forums.openlp.org/discussion/comment/10619/#Comment_10619