Exit db refactor #1482

Job	Run time
check	51s
clippy	52s
audit	19s
rustfmt	11s
test	2m 56s
cross-armv7	53s
cross-aarch64	1m 4s
cross-mipsel	48s
cross-mips	43s
integration-test-five-nodes	26m 23s
integration-test-debts	26m 39s
integration-test-eth-payments	21m 31s
integration-test-multi-exit	21m 44s
integration-test-althea-payment	25m 4s
integration-test-validate-contract	22m 25s
	2h 32m 23s

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