Upgrade to Grails 3.0

[w32blaster]

Migrate project to new version of Grails

• [ ] fix the external configs. Discussion is here

[w32blaster]

Here is a guide: http://grails.github.io/grails-doc/3.0.x/guide/upgrading.html

Here is a good article about what is new in Grails 3: http://www.mscharhag.com/2015/04/whats-new-in-grails-3.html