Correct BMP creation on Linux (PR #1014)

Enable BMP Header packing on all compilers.
Add virtual function to FrameBase to select where to save screenshots.

source/Windows/Win32Frame.cpp

@@ -620,3 +620,9 @@ BYTE* Win32Frame::GetResource(WORD id, LPCSTR lpType, DWORD dwExpectedSize)
 
 	return pResource;
 }
+
+std::string Win32Frame::Video_GetScreenShotFolder()
+{
+	// save in current folder
+	return "";
+}