Add the ability to run as task file at startup. Add new model conversion task that requires an OpenGL context. Add ability to use FileVerifier and DirectoryVerifier on files that don't exist (#3612)

data/tasks/convertmodel.task

@@ -0,0 +1,7 @@
+return {
+  {
+    Type = "ConvertModelTask",
+    InputFilePath = "< in path >",
+    OutputFilePath = "< out path >"
+  }
+}