Deliver status information using server-sent events #1698

Job	Run time
Build Echidna on ubuntu-20.04	19m 35s
Build Echidna on macos-latest	34m 48s
Build Echidna on windows-latest	26m 36s
Test with solc 0.4.25 on ubuntu-latest	5m 0s
Test with solc 0.5.7 on ubuntu-latest	5m 44s
Test with solc 0.6.12 on ubuntu-latest	4m 27s
Test with solc 0.7.5 on ubuntu-latest	4m 0s
Test with solc 0.4.25 on windows-latest	6m 28s
Test with solc 0.5.7 on windows-latest	6m 14s
Test with solc 0.6.12 on windows-latest	8m 17s
Test with solc 0.7.5 on windows-latest	6m 16s
	2h 7m 25s

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