ImpIement convolutional VAE.

[vitskvara]

Implement encoder/decoder constructor.

Implement loglikelihoods etc. for 4D tensors.

Make sure everything works on GPU.

[vitskvara]

Should the conv_encoder and conv_decoder functions be part of this package or in GMExtensions.jl?

[vitskvara]

Convolutional decoder output has to be taken care of in ConditionalDists.jl.

[nmheim]

I vote for GMExtentsions :)

[vitskvara]

Moved to GMExtensions.