Add minibatch support for nn.JoinTable and nn.SplitTable

The method setNumInputDims allows forwarding both minibatch and
non-minibatch tensors through the same module.
If this method is not used, the behaviour of these modules is the
same as before.
Remove setNumInputDims method in JoinTable and SplitTable

Now nInputDims is an optional parameter in the constructor of these modules.
Merge pull request #17 from sergomezcol/master

Add minibatch support for nn.JoinTable and nn.SplitTable