Handle sequence of json time series for Fitbit

[vincentvanhees]

Fixes #76

additionally unrelated to the above: This PR ensures that light data is also extracted from PHB.

Checklist before merging:

• Existing tests still work (check by running the test suite, e.g. from RStudio).
• Added tests (if you added functionality) or fixed existing test (if you fixed a bug).
• Updated or expanded the documentation.
• Updated release notes in NEWS.md with a user-readable summary. Please, include references to relevant issues or PR discussions.
• Added your name to the contributors lists in the DESCRIPTION file, if you think you made a significant contribution.