Change object names in responses

[bonaparten]

Description

Reduce to only two kinds of response:

 - response
    - result[]

and

- response
  - groupByResult[]
    - groupByObject: string[]
    - result[]

Corresponding issue

Closes #16

New or changed dependencies

Checklist

• [x] My code follows the code-style rules, and I have checked on the static analyses ~- I have commented my code~ ~- I have written javadoc (required for public methods)~ ~- I have added sufficient unit and API tests~
• [x] I have made corresponding changes to the documentation
• [ ] I have updated the CHANGELOG.md
• [ ] I have adjusted the examples in the check-ohsome-api script or created an issue in the corresponding repository. More Information here.

[mcauer]

What about #84 ? Is this s.th. different or will it be included here?

[bonaparten]

It could be included here, but we didn't discuss it further since these are all breaking changes that we will introduce with the release 2.0 of the ohsome API. This will be released most likely after summer. So some time is still to come.