GUACAMOLE-288: Add support for multi-monitor connections on RDP.

[corentin-soriano]

What works:

• Display each monitor in separate window.
• Keyboard and mouse events.
• Clipboard (bidirectionally).
• Notify guacd of changes on window load or unload (automatic resize).
• Display user consent button to switch all window on fullscreen when the main window fullscreen is enabled.
• All monitors are on the size of the main window and ordered from left to right (left monitor is the primary).
• Auto scaling on secondary monitors (scaling on mouse moves too).
• Handle CTRL+ALT+SHIFT in secondary monitors (open the menu on the main window).
• Close secondary monitor on client disconnect.
• Admin can limit the usage of multi-monitors on each connection.

To improve:

• Drag item from one window to another without having to release the click and resume on the other side.
• Rendering all content of all monitors on each window (overflow: hidden; :) ).
• Improve mouse move limit.

Add new monitor:

Multiple monitors opened: