Unify config path usage in RESTAPI (and all of Tuktu)

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1. Some actions require the config path to be stripped of its .json file extension (e.g. starting / stopping flows by config path), some require it to be present (e.g. storing new configs / removing configs).
   I would argue the file extension should be present everywhere (maybe only strip it in the frontend for readability).
2. Additionally, for some actions a preceding '/' in front of the path is optional (e.g. storing new configs / removing configs), others need to be consistent within itself (starting / stopping flows by config name), while the automatically started analytics scripts have it, so if you argue for consistency you could say that it's required.
   Again, I would argue we should normalize paths, that includes file extensions as mentioned above, and slashes (or no slashes) in front of the path. Could use Java 8's Paths to do so.
3. Another aspect where it is not unified is with REST API urls, for some it's part of the query parameters, with others it's not.
   Here I would argue that it should not be part of the query parameters, but always be part of the request's content.

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You closed the wrong issue.