GPII-434: General cleanup and rationalisation for Kettle 

all test infrastructure definitions placed in namespace "kettle.test" with actual tests in "kettle.tests" - test infrastructure now loads automatically with the module - grunt tasks for linting, together with all files linted revealed various implementation problems with tests. Added gpii-grunt as a dev dependency in order to get access to "dedupe-infusion" task. Clear distinction made between "tests in the Kettle environment" and "tests based around a Kettle server" - former are bootstrapped with kettle.test.bootstrap, and latter with kettle.test.bootstrapServer
Should we at least check for the presence of a getImpl invoker at some point prior to this line (since it must be provided by concrete DataSource subgrades)? Or, dare I say it, does our grade system need some means by which a grade can be defined as incomplete?