provide wb_copy_cells. closes #282

[JanMarvin]

There are a few things related that can be addressed in the future

• further tweaks to wb_copy_cells() maybe something like Excels apply style option.
• further tweaks to wb_data() (it was a quick draft to allow mschart() inclusion and maybe colNames should be moved to attributes)
• tweaks to wb_clone_worksheet(). next_sheet() always returns sheets named next_sheet.

library(openxlsx2)

wb <- wb_workbook()$
  add_worksheet()$
  add_data(x = mtcars)$
  add_fill(dims = "A1:F1", color = wb_color("yellow"))

dat <- wb_data(wb, dims = "A1:D4", colNames = FALSE)

wb$
  # 1:1 copy to M2
  clone_worksheet(old = 1, new = "Clone1")$
  copy_cells(data = dat, dims = "M2", as_value = FALSE, as_ref = FALSE, transpose = FALSE)$
  # 1:1 transposed copy to A20
  clone_worksheet(old = 1, new = "Clone2")$
  copy_cells(data = dat, dims = "A20", as_value = FALSE, as_ref = FALSE, transpose = TRUE)$
  # reference transposed copy to A20
  clone_worksheet(old = 1, new = "Clone3")$
  copy_cells(data = dat, dims = "A20", as_value = FALSE, as_ref = TRUE, transpose = TRUE)$
  # value copy to A20
  clone_worksheet(old = 1, new = "Clone4")$
  copy_cells(data = dat, dims = "A20", as_value = TRUE, as_ref = FALSE, transpose = FALSE)