* Add checkpoint progress tracking for evalute_ppo. Now when specified with a checkpoint directory,
* Evaluate_ppo will evaluate checkpoints in chronological order, and constantly check for new checkpoint.
* Add tensorboard visualization to both train_ppo and evaluate_ppo
* Add video generation for navigation episode evaluation. Generated videos can be either saved locally or visualized through tensorboard.
* Add shortest path visualization

Fix issue with POINTNAVV1 fix.

SimulatorActions is no longer an enum. It is an extendable singleton. It allows you to extend the action space but it is quite strict about it. Actions cannot be put on different ints, actions cannot be remove.
There is now a registry for action space configurations.

* Modify partitioning logic to handle left-over scenes due to integer division

* Generalize PPO with both PointNav goal sensors
* generalize simple agents and fix lint
* Removed dataset specific nodes

Expose other measures through get_info in NavRLEnv

- add config option NUM_SAMPLE_EPISODE, with default value -1 that
indicates use all episodes. When set value to non-negative integer,
pointna_dataset will sample the specified number of episodes.
- fix the functionality of merging multiple config files. Now can specify
more than one config file like this
	--task-config "a.yaml" "b.yaml"

* 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.

Renamed baselines folder to habitat_baselines

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

* Made simple agents suitable for challenge submissions.

* Addressed the comments, chaned flag names, switched to benchmark

* Removed .swp file, added swp to gitignore.

* Compatability with habitat-sim#6

* Fix formatting

* Just use the quats to rotate thing

* Burn in looks good

* Fixup newly merged code wrt. this PR

* Nits

* Fixup quaternion usage

* Add TODO