Basic data table server with column selection option

This is for the usual iso_get_... aggregation functions.

data_table_server(
  input,
  output,
  session,
  settings,
  get_variable,
  get_iso_files,
  is_visible,
  get_data_table,
  get_data_table_columns
)

Arguments

get_variable	reactive function returning the selected variable
get_iso_files	reactive function returning the currently loaded isofiles
is_visible	reactive function determining visibility of the auxiliary boxes
get_data_table	a regular or reactive function taking iso_files and a list of column names to retrieve the data table
get_data_table_columns	a regular function taking iso_files and returning a vector of data table columns