added support for grouped bars in e_error_bar

[helgasoft]

fixing #120 and #103 - thanks to @matthias-a for the right direction and @JohnCoene for readiness to help

[helgasoft]

Found a bug. When data is without categories, legend click does not hide error bars along with the main bars.
To reproduce:

  df <- data.frame(
    x = factor(c(1, 2)),
    y = c(1, 5),
    upper = c(1.1, 5.3),
    lower = c(0.8, 4.3)
  )
  df %>%
    e_charts(x) %>%
    e_bar(y) %>%
    e_error_bar(Lower, Upper)

This is due to a missing error bar name, and here is the fix

#  in e_error_bar_  (add_.R) replace:
      if (!is.null(name)) {
        nm <- name
      } else {
        nm <- .name_it(e, NULL, name, i)
        # nm <- paste(nm, "error")	    # comm.out: now adopts main bar's name
        nm <- trimws(nm)
      }
# with:
      nm <- .name_it(e, e$x$opts$series[[i]]$name, name, i)

[JohnCoene]

Thank you for this!