[host] Windows: Implemented service to launch LG as the SYSTEM user

Experimental, use at your own peril!

This commit adds the ability for the LG host to install and launch with
Windows as a system service.

To install simply run `looking-glass-host.exe InstallService` or
conversely to uninstall `looking-glass-host.exe UninstallService`.

host/platform/Windows/CMakeLists.txt

@@ -7,6 +7,7 @@ include_directories(
 
 add_library(platform_Windows STATIC
 	src/platform.c
+	src/service.c
 	src/mousehook.c
 )
 
@@ -23,6 +24,9 @@ target_link_libraries(platform_Windows
 	"${PROJECT_BINARY_DIR}/resource.o"
 	lg_common
 	capture
+
+	userenv
+	wtsapi32
 )
 
 target_include_directories(platform_Windows