Add mobilenetv2ssdlite512 test.

Works for CuDNN, not for tensorRT.
Modified channels in second convolution for classification headers from 126 to 486, when changing size from 300 to 512.
Added size 512 SSD specs and support to COCO dataset (81 classes, first BACKGROUND due to repo for training).
Refactoring class names.

Signed-off-by: Micaela Verucchi <micaelaverucchi@gmail.com>

demo/demo/demo.cpp

@@ -44,7 +44,7 @@ int main(int argc, char *argv[]) {
             cnet.init(net);
             break;
         case 'm':
-            mbnet.init(net);
+            mbnet.init(net, 512, 81);
             break;
         default:
         FatalError("Network type not allowed (3rd parameter)\n");