integrate semi-supervised autoencoder method into AITom

[xulabs]

@xiangruz ask MCDS student to do the following

add the code under following module
aitom/aitom/classify/deep/supervised/cnn/semi/autoencoder

use existing functions in AITom as much as possible

write a tutorial and add to
https://github.com/xulabs/aitom/blob/master/tutorials/012_semi_supervised_autoencoder.py

prepare page and figures to be added to
https://github.com/xulabs/projects/semi_supervised_autoencoder/readme.md

write 10 - 20 slides and add to google drive