* Made isort for CI check only

* Added badges

Updated baselines readme, fixed links, added link to checkpoints.

* Fix the citation

* Caps

Asterisk for co-first author messes up alphabetical ordering in references section.

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

Our registry pattern is far from idea and thus we haven't used it consistent. This PR aims to resolve this by copying the registry pattern used in Pythia (as it is much nicer) and then registering all current measures and sensors and using the register to query for those instead of getattr as this is a more clearly extendable pattern (as compared to monkey patching).

* Update main README to properly install gym

* Update baseline README for gym install

* add extras_require in setup.py

* add exclude in setup.py for baselines

* add pytest as requirement

* Implement accessing setup() params within custom commands

Config system improvements: compositional config, added scenes_dir, removed config_dir, fixed eqa test (#77)

* Added scenes_dir parameter to Config to have no requirement of data symlink or data directory in working directory. scenes_dir will be used as prefix for scene_id during episodes dataset loading.
* Added overwriting options argument to get_config that unblocks parameter sweeping and experimentation capabilities from command line
* config_file path can be comma separated list of configs that will be merged in exact order. That will help to use separate configs for dataset specification and sensors setups. String with commas was chosen because that make it easy to pass list of configs as script argument.
* To make habitat-api easier to as package we decided to get rid of forcing loading of configs from config_dir param
* fixed unit test caused by latest habitat-sim update
* Added support of config list, corrected scene_path, added overwriting options, added EQA dataset changes, adopted quaternion suggestion
* Fixed headers