Err-stackstorm

Added
- Split unit tests in separate test files.
- Added linting to CircleCI
- Added try/except blocks around plugin configuration code to improve installation and startup
experience when there are errors in the configuration.

Changed
- Fixed dictionary keys to reference 'apikey' consistently.
- Switch CircleCI from calling pytest directly to using Makefile.
- Dropped using sseclient-py in favour of btubbs sseclient.
- Corrected references to apikey configuration.

Removed

Added
- unit tests for more low level objects used by err-stackstorm.

Changed
- updated makefile to be better adapted to CircleCI's build process. (Still a work in progress)
- numerous documentation updates to improve installation process for new users.
- documented errbot's ACL features.

Removed
- removed unused code for keyring and vault.

Added
- Correctly support action-alias acknowledge enabled flag in StackStorm API.
- Support appending the execution `web_url` to action-alias acknowledgement message.

Changed
- Fixed exception raise in log message when err-stackstorm isn't able to fetch a valid StackStorm user token.

Removed
- removed dependency for st2client to be able to use requests>=2.20. This avoid conflicts with popular chat backends.

Added
- setup.py to be able to install plugin from the command line.
- Dockerfile to build an image and run err-stackstorm from within a Docker container. (alpine linux based)
- Support for Out-of-Bands authentication.
- Support for formatting with XMMP backend.

Changed
- Updated err-stackstorm python module requirements.

Removed

Added


Changed
- Readme spelling corrections.
- Aligned `api_url`, `auth_url` and `stream_url` with the [StackStorm API](https://api.stackstorm.com/)


Removed
- remove `base_url` and `api_version`, they're now calculated from the `api_url`, `auth_url` or `stream_url`.