[neuralnet] Support deallocate of tensors

[neuralnet] Support deallocate of tensors

Support deallocate and allocation of tensors from the neuralnet.

Also perform the deallocation of tensors after each train run.
Once a training is performed, the memory associated for that training
except the weights variables will be freed.

The memory associated with inference will not be freed until freed manually.
This will require calling deallocate() with the model object.
Note that calling a train() after inference() will free the inference memory
and the train will allocate its own memory which will be freed at the end
of the training.

**Self evaluation:**
1. Build test: [x]Passed [ ]Failed [ ]Skipped
2. Run test: [x]Passed [ ]Failed [ ]Skipped

Signed-off-by: Parichay Kapoor <pk.kapoor@samsung.com>