Fix to several smaller issues relating to visualreport, diary handling, and simplifying usage of MVPA parameters

[vincentvanhees]

In this PR several smaller fixes:

• Speeds up loading of activity diary, mainly relevant for large datasets, fixes Too slow loading of activity diary #1250
• Skips loading of activity or sleeplog diary when input diary has not changed, fixes Too slow loading of activity diary #1250
• Corrects determining how many recordings should be in part 2 csv report, fixes Correct determining how many recording should be in part 2 csv report #1252
• Improves handling of optional diary imputation code as stored in advanced format sleeplog and adds documentation for this Handling optional diary imputation code in advanced format sleeplog #1251
• Visualreport is now able to handle recordings with only 1 valid day. Outstanding action points for recently added visualreport #1246
• Simplifies MVPA parameter specification for part 2 by using the part 5 values when not specified, fixes Reduce number of parameters needed to configure PA levels #1247
• Update Cookbook.Rmd to better communicate that the example currently shown there are specific to externally derive epoch data and NOT for raw accelerometer data. fixes Running GGIR on the UK Biobank Research Analysis Platform #1248

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).
• Clean code has been attempted, e.g. intuitive object names and no code redundancy.
• Documentation updated:
  • Function documentation
  • Chapter vignettes for GitHub IO
  • Vignettes for CRAN
• Corresponding issue tagged in PR message. If no issue exist, please create an issue and tag it.
• Updated release notes in inst/NEWS.Rd 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.
• GGIR parameters were added/removed. If yes, please also complete checklist below.