Support for GAE embeddings

[nmilosev]

Support for:

• Non-variational non-linear autoencoders
• Variational non-linear autoencoders
• Non-variational linear autoencoders
• Variational linear autoencoders

Other changes:

• added classification and clustering examples (tests)
• added argparse subparser for gae
• added pytests for gae
• reformatted repo with black

[nmilosev]

Sam sebe proverio, sve je super!