* cannot remove bill type (Kayo) - OR (TODO): modify it to yearly from monthly

* can put in dumb dates - DO SOME INPUT VALIDATION, *sigh*
    - e.g. 0026-02-19 for a Gas bill

* kayo bills are wrong in between normal bills

* added an electricity bill by accident for 2018, that kills lots :(
    - something to do with missing year of data in quarterly bills - still an issue

* if change a bill (like Amazon), then its future estimates don't update
    - recalc does fix, so a simple delete future bills for this bill type and
      re-estiate will do it, BUT, its a simple POST now...
      I think a re-write of functions in bills may be needed, so that we can
      pull out future estimates based on growth (that may need to change due to
      this changed amount), etc.
    - also occurs if we delete a bill
    -- but on the +ve side, changing growth toggle, resets future bills - 
        so can call UseGrowth( bt_id )
        SO only missing bit would be to recalculate growth based on existing
        bills for this bill type.... SO, may not need to redo code everywhere,
        but should consider it anyway