add suite dsl

[christophsturm]

there should be some kind of api to describe what tests to run, in what order, and what test dependencies to eagerly load.

(for example to run unit test before integration tests). but also just simply to run a combination of tests that is useful for the current thing that you are working on (one single test, or one test file)

playing around with the api in #177

[mervyn-mccreight]

for example to run unit test before integration tests

couldn't anyone do that with defining separate test source sets for e.g. integration tests and define the task-order in the gradle build?