fetch forwarder address from swap contract

[stubbrn]

closes #365

What should I do for mainnet? SwapCreatorAddr is "0x" and ForwarderAddr is used in CheckForwarderContractCode

https://github.com/AthanorLabs/atomic-swap/blob/ea8bae1416c2c4fad8a5a30cb03118675a52994e/common/config.go#L70-L72 https://github.com/AthanorLabs/atomic-swap/blob/ea8bae1416c2c4fad8a5a30cb03118675a52994e/ethereum/check_swap_creator_contract.go#L116

[codecov[bot]]

Codecov Report

Patch coverage: 45.45% and project coverage change: -0.29 :warning:

Comparison is base (606f80f) 59.13% compared to head (aff243e) 58.84%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #404 +/- ## ========================================== - Coverage 59.13% 58.84% -0.29% ========================================== Files 120 120 Lines 10723 10733 +10 ========================================== - Hits 6341 6316 -25 - Misses 3689 3715 +26 - Partials 693 702 +9 ``` | [Impacted Files](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/404?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [common/config.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/404?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y29tbW9uL2NvbmZpZy5nbw==) | `84.76% <ø> (-0.15%)` | :arrow_down: | | [cmd/swapd/main.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/404?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y21kL3N3YXBkL21haW4uZ28=) | `68.02% <45.45%> (-0.65%)` | :arrow_down: | ... and [8 files with indirect coverage changes](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/404/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None)

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[noot]

since the mainnet contract isn't deployed yet, we should probably merge this after that's done (which should be very soon!)

[dimalinux]

Thanks for the work and getting us to figure out the small details for the complete fix! I'm closing this PR, as https://github.com/AthanorLabs/atomic-swap/pull/427 ending up fixing the issue.