Test continuous ingest

The problem of resolving diferences between versions should be solved server-side with update conflict mechanism sshoc-marketplace-backend#85 (closed) Now we need to test, if it does what we want it to.

For this we decided following procedure:

1. make a dummy source S for one of our ingest pipelines
2. run first ingest of S into dev
3. do manual changes x on some items I from S in the marketplace
4. do different changes y to the same items I directly in S.
5. do a reingest of source S using methods described in sshoc-marketplace-backend#85 (closed)
6. evaluate the responses of the methods
7. evaluate what happens to items I

(join the evaluation party: @anowak, @klaus.illmayer, @lbarbot, @matej.durco )