Make clipboard optional for dance_report()

[LucyMcGowan]

I am trying to use dance_report() in RStudio Cloud, but it doesn't play nicely with the clipboard 😢. Would you be okay with this change? If so, I can submit a PR.

copy_base64 <- function(clip = TRUE) {
  enc_string <- base64_enc(serialize(dance_tbl(), NULL))
  if (clip) {
   write_clip(enc_string)
  } else {
   enc_string
 }
} 

[seankross]

Yeah looks good!