Initialise CSystemUtils' singleton in the three light, transform and model tests

Also fix README

test/envs/opengl/README.txt

@@ -1,7 +1,7 @@
 Test programs for OpenGL engine:
   - texture_test -> multitexturing test with 2 textures (included as files: ./tex1.png, ./tex2.png)
   - model_test -> simple model viewer to test model loading
-    usage: ./model_test {dxf|mod} model_file
+    usage: ./model_test {old|new_txt|new_bin} model_file
       second argument is the loaded format (DXF or Colobot .mod files)
     requires ./tex folder (or symlink) with Colobot textures
     viewer is controlled from keyboard - the bindings can be found in code

test/envs/opengl/light_test.cpp

@@ -365,6 +365,9 @@ int SDL_MAIN_FUNC(int argc, char *argv[])
 {
     CLogger logger;
 
+    CSystemUtils* systemUtils = CSystemUtils::Create(); // platform-specific utils
+    systemUtils->Init();
+
     PREV_TIME = GetSystemUtils()->CreateTimeStamp();
     CURR_TIME = GetSystemUtils()->CreateTimeStamp();
 

test/envs/opengl/model_test.cpp

@@ -265,6 +265,9 @@ int SDL_MAIN_FUNC(int argc, char *argv[])
 {
     CLogger logger;
 
+    CSystemUtils* systemUtils = CSystemUtils::Create(); // platform-specific utils
+    systemUtils->Init();
+
     PREV_TIME = GetSystemUtils()->CreateTimeStamp();
     CURR_TIME = GetSystemUtils()->CreateTimeStamp();
 
@@ -273,7 +276,7 @@ int SDL_MAIN_FUNC(int argc, char *argv[])
 
     if (argc != 3)
     {
-        std::cerr << "Usage: " << argv[0] << "{old|new_txt|new_bin} model_file" << std::endl;
+        std::cerr << "Usage: " << argv[0] << " {old|new_txt|new_bin} model_file" << std::endl;
         return 1;
     }
 

test/envs/opengl/transform_test.cpp

@@ -243,6 +243,9 @@ int SDL_MAIN_FUNC(int argc, char *argv[])
 {
     CLogger logger;
 
+    CSystemUtils* systemUtils = CSystemUtils::Create(); // platform-specific utils
+    systemUtils->Init();
+
     PREV_TIME = GetSystemUtils()->CreateTimeStamp();
     CURR_TIME = GetSystemUtils()->CreateTimeStamp();