Initial commit with new slim-test-helpers dependency

Temporarily remove all but the file store tests so that we can isolate
troubles as we implement the new client/app bootstrap split.
Update composer file with latest slim-test-helpers
Convert integration tests to use test helpers

This commit converts the integration tests to use the test helpers. I’m
not entirely satisfied with the local web test case class, but it is
fairly tidy and centralized to the bootstrap and makes the test files
trim.
Merge pull request #10 from there4/slim-test-helpers

Use slim test helpers from test helpers repo