Fix currency formatting

[wernerkrauss]

somehow related to #779 some more formatting for different prices in the backend.

For formatting payments see https://github.com/silverstripe/silverstripe-omnipay/issues/244

@wilr and/or @forsdahl please have a look at this PR and merge if possible. I disabled OrderModifier's Amount() method which should be fine IMHO but could possibly break some stuff.

[wilr]

All checks are green so I'm happy

[chromos33]

disabling the Amount method breaks the ShowInTable() function in OrderDiscountModifier in the Discount Module.

[wernerkrauss]

@chromos33 Thanks for reporting this. Can you please try changing OrderDiscountModifier's ShowInTable() method to:

    public function ShowInTable()
    {
        return $this->Amount > 0;
    }

so using the magic DB-Field value directly instead of the getter method