Implement cloneWorksheet function to duplicate existing sheets in the workbook

[kainhofer]

Implement a cloneWorksheet function to create a full copy of an existing worksheet and add it as a new worksheet to the workbook.

This pull request is my current status, which I'm using myself regularly. What is working:

• Content
• Styles are properly copied.
• Tables
• images
• charts (data range is adjusted to point to the cloned sheet, too)

What is missing:

• probably drawings, comments, etc.
• pivot tables

For these, I suppose some XML strings stored in the fields of the Workbook class need to be duplicated + modified and new IDs assigned I don't have the insight into the full xlsx file format, so I have not yet figured out which parts need to be duplicated and where an ID needs to be changed. For the styles I think I got it right (at least it seems to be working)

This pull request is intended to fix/implement issues #255 and #330. This replaces PR #355

[codecov[bot]]

Codecov Report

Merging #483 into master will decrease coverage by 0.87%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #483      +/-   ##
==========================================
- Coverage   60.23%   59.35%   -0.88%     
==========================================
  Files          30       30              
  Lines        7142     7108      -34     
==========================================
- Hits         4302     4219      -83     
- Misses       2840     2889      +49

Impacted Files	Coverage Δ
R/worksheet_class.R	73.64% <ø> (+0.36%)	:arrow_up:
R/wrappers.R	42.4% <0%> (-0.22%)	:arrow_down:
R/WorkbookClass.R	52.38% <0%> (-2.88%)	:arrow_down:
src/write_data.cpp	60.76% <0%> (-3.8%)	:arrow_down:
src/write_file_2.cpp	0% <0%> (-1.43%)	:arrow_down:
R/HyperlinkClass.R	93.02% <0%> (-0.98%)	:arrow_down:
R/workbook_write_data.R	82.35% <0%> (-0.85%)	:arrow_down:
src/read_workbook.cpp	90.55% <0%> (-0.39%)	:arrow_down:
R/writeDataTable.R	71.59% <0%> (-0.32%)	:arrow_down:
R/helperFunctions.R	75.31% <0%> (-0.25%)	:arrow_down:
... and 13 more

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[ycphs]

Hi,

I added your PR into my fork ycphs/openxlsx. I am looking forward to get your support for publishing an updated version of the package on cran.