Use in-process testing of Dagger

[alex2069]

Currently for simplicity Dagger is tested using an external script runDaggerVersionTests.sh that simply loops over dagger versions, rebuilding the demo app performing connected tests with different versions of dagger. This processes is extremely slow, adds bloat to the demo, and doesn't provide a convenient means of investigating errors. Additionally, at present in order to test alternative Dagger configurations the demo app would need to be altered, which would effectively destroy the original "tests" in the process.

The test project can run kapt and compile in-process and take advantage of a proper test environment. This would also allow testing of custom Dagger configurations outside of the constraints of the demo's contrived setup.