Add example app with Snowplow interface

[Jack-Keene]

Add an example using the new Snowplow interface

[Jack-Keene]

EG

# Configure Emitter
    emitter_config = EmitterConfiguration()
    emitter_config.buffer_size = 5

    # Configure subject
    subject = Subject()
    subject.set_user_id("uid")

    Snowplow.create_tracker(
        namespace='ns',
        endpoint="http://localhost:9090",
        app_id="app1",
        emitter_config=emitter_config,
        subject=subject
    )

    Snowplow.get_tracker('ns').track_page_view("https://www.snowplow.io", "Homepage")
    Snowplow.trackers['ns'].track_page_view("https://www.snowplow.io", "Homepage")
    Snowplow.trackers['ns'].track_page_view("https://www.snowplow.io", "Homepage")
    Snowplow.create_tracker(
        namespace='ns2',
        endpoint="http://localhost:9090",
        app_id="app1",
    )

    Snowplow.trackers['ns'].flush()