Setup icon (i,j coordinates in ImGui Toolkit) for each Source class, and

use this icon in GUI to indicate the type of class.

DeviceSource.cpp

@@ -512,6 +512,13 @@ DeviceConfigSet Device::getDeviceConfigs(const std::string &src_description)
 }
 
 
+glm::ivec2 DeviceSource::icon() const
+{
+    if ( device_.find("Screen") != std::string::npos )
+        return glm::ivec2(19, 1);
+    else
+        return glm::ivec2(2, 14);
+}