MultiGPU training:

speed is significantly increased.
fixed CUDNN_STREAM errors.

Trainer: added key 'b' : creates a backup even if the autobackup is disabled.

models/Model_Quick96/Model.py

@@ -163,7 +163,7 @@ class QModel(ModelBase):
 
         masked_training = True
 
-        models_opt_on_gpu = len(devices) == 1 and devices[0].total_mem_gb >= 4
+        models_opt_on_gpu = len(devices) >= 1 and all([dev.total_mem_gb >= 2 for dev in devices])
         models_opt_device = '/GPU:0' if models_opt_on_gpu and self.is_training else '/CPU:0'
         optimizer_vars_on_cpu = models_opt_device=='/CPU:0'