Limit requirements search scope to habitat_baselines folder.

Adds documentation for habitat-api, to view the docs follow instructions in docs/README.md and view the html files from the build folder.

* Builds and installs habitat-sim with python setup.py install
* Added pytorch installation and running habitat baseline test in prediction mode. That maybe too much of testing, but decided to keep it for now.
* Have ideas how to speed up and parallelize jobs. Will follow up in next PRs.
* Run isort and black on whole code to make it happy.
* Includes parallelization of installation steps and use files as flags that step is finished. CircleCI has no good way to parallelize steps and have dependencies one the same machine.
* Cache is used to save conda dependencies installed and build simulator based on commit SHA.

* add extras_require in setup.py

* add exclude in setup.py for baselines

* add pytest as requirement

* Implement accessing setup() params within custom commands

Include data files into package