Added --param cmdline param to modify UG intenals

These options are now available:
decoder - to force user selected decoder (eg. libavcodec instead
of gpujpeg, which would be chosen by default)
drop-policy - to allow non-blocking put frame (effectively drops
frames that cannot be displayed immediately, eg. when display
frame rate is lower than video frame rate)

src/host.cpp

@@ -58,6 +58,8 @@ bool ldgm_device_gpu = false;
 
 const char *window_title = NULL;
 
+std::unordered_map<std::string, std::string> commandline_params;
+
 static void common_cleanup()
 {
 #ifdef USE_MTRACE