construct xt Config using several functions

[MikeBadescu]

• setDefaultConfig() to create $.default
  • first arg: xt_lst, must be present
  • second argument ...; augments if NULL from .XT$.default
    • for now, populate .XT$.default based on onetable
  • modifies $.default if present, adds $.default if missing in xt_lst
• setOptionsConfig() to create $.options
  • first arg: xt_lst, must be present
  • second argument ...; augments if NULL from .XT$.options
    • for now, populate .XT$.options based on onetable
  • modifies $.options if present, adds $.options if missing in xt_lst
• initConfig()
  • takes no arguments
  • returns an xt list (xl_lst) with only two fields: .default and .options
  • calls setDefaultConfig() and setOptionsConfig() w/o arguments
• setColConfig() to update a column configuration
  • first arg is xt_lst, must be present
  • second argument ...; complains if it finds a named argument not in $.default
• checkConfig(xt, allow_mode = FALSE) to check an xt Config (a list from xt_lst)
  • all fields starting with . must be recognized (these are allowed fields, listed in .XT)
  • there should be only one .default and .options (multiple other . names allowed)
  • dot fields must have col_name == NULL
  • names in xt list must match col_name for all the other fields (non dot fields, user columns)
  • non dot names must be unique and contain a-z A-Z 0-9 _ (and no spaces)
  • class, ui_name must be present (for all the not dot fields, NA not accepted)
  • widget, if present, must be either it's name (a string) or a list with the first argument name
    • the name must be on the allowed list in .XT
  • there should be no mode names (dt, edit, add) within col config unless allow_mode = TRUE