Make Staking DApp work with transferAndCall function

[varasev]

Motivation

I recently updated the StakingAuRa contract so that it supports staking with transferAndCall function along with the stake function. We need this to switch POSDAO from the non-bridged STAKE token contract to the bridged one.

Please, don't merge this until we switch the StakingAuRa contract to the new implementation. I'll let you know when that happens. Done: https://github.com/poanetwork/posdao-contracts/releases/tag/v0.1.9

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build f8e9f8b4f3ab3464e0b633a6518e21dc51b9169e-PR-3498

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 21 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+1.5%) to 66.99%

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Files with Coverage Reduction	New Missed Lines	%
lib/block_scout_web/channels/stakes_channel.ex	21	0%

Totals
Change from base Build 522fa5a5edbfa052a20213fd6ec7d0808497f71c:	1.5%
Covered Lines:	2070
Relevant Lines:	3090

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💛 - Coveralls

[varasev]

Now this PR can be approved and merged - we released a new version of the StakingAuRa contract: https://github.com/poanetwork/posdao-contracts/releases/tag/v0.1.9