Prevent reset offer values after switch to same currency payment account

[ghost]

Fixes #5973

When we switch to same currency account we don't need to reset volume, minVolume, price and marketPriceMargin.

When we switch to different currency account onCurrencySelected is invoked, so these params are being reset.

Pull request applies to "create offer", "edit offer" and "duplicate offer" views.

Demo:

1. Before:
   

2. After:
   

[chimp1984]

I think that requires good testing. The validation checks are rather complex and carry already a few bugs. Resetting the values made it easier to not carry over stale validation state after changes. So I think its good to change that, but just want to emphisis the risks.

[ghost]

I agree code around MutableOfferView is quite complex. When I was debugging original issue I set debugger breakpoint on updateButtonDisableState method and I saw it was invoked 5 or 6 times after changing trading account (in ideal world there should be single call).

Sure - I'll try to prepare testing scenarios that covers changes in this pull request. If you see any edge cases that I should include don't hesitate to share them here.

[ripcurlx]

I did try some scenarios and removing this reset code didn't make anything worse, but I found a different bug.

If you switch in create offer between payment methods that share the same supported currency and the new payment method has a different default currency set, the price related fields are not updated properly.

@xyzmaker123 Do you want to prepare a PR for this as well?

[ripcurlx]

ACK - Tested it on Regtest

[ghost]

@ripcurlx Sure - I can try to fix this issue. If you don't mind please prepare appropriate issue and assign me (for better tracking).