fix: Offline Currency Payout Improvements

[phroggster]

Description of the Change

• Currency payouts would stop paying out while offline once any currency had a zero offline payout or was left at the defaults.
  • Changed it to keep checking additional currencies.
• As well, the model's offline property is an empty string if the checkbox is checked, then unchecked in the add or edit currency model (addOrEditCurrency.js/html).
  • ~~I don't want to expand the Currency type definition in currency-access.ts, but we might want to.~~ Edit: I didn't.
  • Fixed this in (attempt two, in) the controller's save function to undefine the value if it's null or empty.

Applicable Issues

#2796. #2801

Testing

Minimal, but yes. Verified bugs existed, then verified that this fixed them.

Screenshots

N/A

[phroggster]

~~Ebiggz / et. al: will you let me know if you'd rather I actually overwrite the model's empty string .offline property to a 0 or null in addOrEditCurrency.js when it's saving the currency instead of this approach? I feel hackish about any answer to this at this point, and am unsure of what's the least-worst solution.~~

[phroggster]

I have reverted my prior 2801 commit, and gone ahead and fixed it properly. Retested with every variation that I could come up with to break it, and this works better, and is better for the outside world.