start the integration test "infrastructure"

There's no test yet, only the system to bootstrap the docker images that are
required to execute tests.

The general idea is to have multiple configuration files in the test/assets
directory that are used to simulate different configurations. These configurations
are executed from a docker image running a local copy of xivo-dird.

The Dockerfiles are in contrib/docker/base_test_image and tests

The base_test_image is used to speed up the image generation of the dird-test image

Before testing xivo-dird you must build the base_test_image

make test-setup

Then you can rebuild you test image when you change your local copy of xivo-dird

make test-image

There's an example config in tests/assets/test_csv_backend that can be launched with

make test-csv

This last command is meant as documentation only. The test runner should be able
to launche the docker image with the appropriate configuration file when running.
add a first test example using the csv asset
remove the path from the csv test
Merge remote-tracking branch 'origin/5027-dird-headers-view' into integration-tests
add integration tests for the display configuration
remove the make test-csv target

images are now started by the test runner
rename assets used in integration tests
fix branch name
add integration tests for a configuration with multiple sources from one backend
fix copyright year in a new file
Refactor integration tests

integration tests plumbing is now in base_dird_integration_test
distributed other tests in other modules
handle broken source configuration

if a source configuration is broken, other sources should keep working
add the missing assets for the broken source config tests
add a test for a csv backend with no unique columns
add a test to make sure that dird is not running if it is not configured

not configured meaning no plugins loaded
test that the source_config_dir is respected
add accentuated characters to the csv backend tests
add integration tests for the csv backend with accents
add separator support for the csv backend
Update README.md

Add some information to be able to run the unittests and integration tests