Create a grunt plugin for update-version and set-version commands

[dutchmartin]

Create a grunt plugin out of the duplicate code in the various plug-in repositories for better maintainability
for example:
the grunt custom folder in wp-seo-news has 2 files in it that are identical to the grunt custom folder in wpseo_woocommerce

[dutchmartin]

the branch 1--Create-grunt-plugin-for-custom-tasks currently contains the most of this issue's code, I only need help in checking if all features are present.
Can @atimmer or @moorscode please check this so I can make a PR.