Add --docker-server cli option and standardize options

Summary:
- Add --docker-server option and update docs
- Add gulp-options file to allow overriding `options` in gulpfile.js

Test Plan:
Run `gulp --docker-server`
Run `gulp --node-server`

Reviewers: shadowhand, spaudanjo

Reviewed By: shadowhand, spaudanjo

Differential Revision: https://phabricator.ushahidi.com/D388