Clean up g.part 5

[vincentvanhees]

Given that there are various expansions and enhancements to part 5 (#839, #817, #807, #687) in planning, I am exploring how to first clean up g.part 5 to reduce length and complexity of code.

Draft plan for now:

1. Code to prepare the ts object including essential columns such as diur, ACC. Maybe this part can stay inside g.part5 as it is relevant for all following sub-functionalities.
2. Code to describe data per segment (MM, WW, or shorter segments). Maybe this could be called g.part5_analyseSegment:
3. Code to perform circadian rhythm analyses not dependent on window descriptions, but potentially in need of selecting time window between first wakeup/onset and last wakeup/onset. g.part5_analyseMultiday

Here it would be good to already account for:

• Option to express focus, e.g. focus on part 5 means that all potentially overlapping analysis in part 2 are skipped there.
• Option to run different parts at different resolutions.