Finished MMAL decoder

• MMAL decoder is very slow on Raspberry Pi
• OpenGL renderer supports automatic switching between OpenGL ES and OpenGL
• FFmpeg on Raspberry Pi OS contains an RPI Hwaccel option, which is more performant. It's not documented, so further research is required in order to implement it.

.idea/misc.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="CMakeWorkspace" PROJECT_DIR="$PROJECT_DIR$" />
+  <component name="CidrRootsConfiguration">
+    <excludeRoots>
+      <file path="$PROJECT_DIR$/build-qt59" />
+    </excludeRoots>
+  </component>
   <component name="ProjectPlainTextFileTypeManager">
     <file url="file://$PROJECT_DIR$/AVQt/mainpage.dox" />
   </component>