Feature: overview_tab

[cosimameyer]

• Basic function is added
• Drop missing values

   # Check if there are NAs in the time or id variable
    # (and drop them but warn the user about it)
    if (sum(is.na(dat[[id]])) > 0) {
      warning(
        "There is a missing value in your id variable. The missing value is automatically deleted."
      )
      dat <- dat[!is.na(get(id)), col_names, with = FALSE]
    }