Add automated releases using travis CI

[tomas-polach]

we are currently running this release script manually: https://github.com/archilogic-com/3dio-js/blob/master/tasks/release.js

goal:

enable github's travis CI service to run release script automatically (for master branch only!) on version number change.

to do:

• generate NPM auth token: https://docs.travis-ci.com/user/deployment/npm/
• add travis CI config file .travis.yml to the repo (example: https://github.com/archilogic-com/3dio-website/blob/master/.travis.yml)
• enable travis CI github service in: https://github.com/archilogic-com/3dio-js/settings/installations
• add ENV variables for S3 and NPM in travis CI settings (ask tomas for the S3 keys)
• modify release script to compare release version number from NPM to version number in package.json. continue release script only if version numbers are different. in case they are same: exit release script without error.
• add step to release script preventing the script being run from repositories other than origin
• add build status shield to README.md (for an example see: https://github.com/archilogic-com/3dio-website/blob/master/README.md)

[tomas-polach]

@m-ke this one might be interesting to you? travis CI is similar to jenkins and integrates nicely with github...