[nnstreamer][trainer] Create a queue to construct dataset

[nnstreamer][trainer] Create a queue to construct dataset

- It is dynamically allocated as much as initial queue size and
  continues to use the memory until training is finished.
- The maximum size of the queue is 30, and if the number of samples
  is less than 30, size is number of samples.
- Data received through 'invoke' is strored in queue, and the data
  in the queue is used in the 'data gen callback'. the used data
  is not maintained for epochs.
  For epoch, (number of trin samples + number of valid samples) * epoch
  data should be received.

Signed-off-by: hyunil park <hyunil46.park@samsung.com>