Update cron job to run every 20 minutes

1 minute is too fast. 20 minutes is possibly too.
Add Gulp

Gulp task runner added to the project, featuring jshint tests
Fix lint errors

- Many lint errors were removed
- Trailing white-space in .js files were removed
Expand lint task for all js files

- Lint were expanded to every js file in the project
- Fix lint errors of these files
- Fix trailing white-space in these files
Add support to Travis-ci