[SysApps] Implement the Device Capabilities getDisplayInfo()

This provider is missing an Observer interface for notifications
of displays being connected and disconnected. This is very likely to
be platform dependent and we might need to add platform files.

Currently we only using a static method, but I'm keeping the GetInstance()
for the display monitoring implementation.
[SysApps] Add a simple test for Device Capabilities

Not to self: make a browsertest out of this. :)