- avoid using screen number as display number on Linux
- support for area selection over multiple screens on Linux
- make getFrame null safe
- make video-full-screen mode show in the correct screen
- add the option of "share all screens"
- use x11 api for unix system for sharing screen areas

Gitlab: #160

Change-Id: Ibe47a4150b6a213950a0533d85e8cd7d5d159482