Add support of 0.6.x version of solc compiler

[vbaranov]

Fixes #2957

Motivation

• Add support of 0.6.x version of compiler
• Add istanbul to supported evm list in verification
• increase solc npm package version up to 0.6.1

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 96b6453f-017d-4889-90c5-df28c2c703ea

• 6 of 9 (66.67%) changed or added relevant lines in 2 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.004%) to 75.252%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/explorer/lib/explorer/smart_contract/verifier.ex	0	1	0.0%
apps/explorer/lib/explorer/smart_contract/verifier/constructor_arguments.ex	6	8	75.0%

Files with Coverage Reduction	New Missed Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	2	71.43%

Totals
Change from base Build c86d1745-4ddc-4f80-88f5-bd26fdb594a3:	0.004%
Covered Lines:	5376
Relevant Lines:	7144

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💛 - Coveralls