Add automatic resolution setting based on window size via spice

[marmeladapk]

Potential use cases:

• Moving LG window to another monitor with different resolution
• resizing window to fit another, native application on the same monitor

I work with a single CAD application on Windows and sometimes I need to switch between VM and linux applications.

As a sidenote, thank you for your work on Looking Glass!

[gnif]

This has been requested and rejected multiple times. https://github.com/gnif/LookingGlass/issues/567

Note that funding has been provided and a new version of the host is currently in the research stage that should be able to perform this.