Revamp node wallet scan management to minimize wallet re-scans

[greenhat]

Close #243 Close #250

This PR revamps wallet scans management:

• use only token id in scans (no need for a contract or register values);
• remove scans for "own" oracle and ballot boxes (filter from general scans);
• de-register all scans in import-pool-update command;
• register new scans only on run command (to avoid registering due to missing --data-dir option in other commands);

Added:

• `GenericTokenScan to represent a wallet scan for the given token id.
• NodeRegistryScan for persistent storage and register/de-register with node;
• Switches to newly added ScanId type in ergo-node-interface crate.

[coveralls]

Pull Request Test Coverage Report for Build 4615936160

• 17 of 185 (9.19%) changed or added relevant lines in 14 files are covered.
• 8 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.4%) to 60.265%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
core/src/pool_commands.rs	0	1	0.0%
core/src/pool_commands/test_utils.rs	2	3	66.67%
core/src/cli_commands/prepare_update.rs	0	3	0.0%
core/src/scans.rs	0	3	0.0%
core/src/api.rs	0	6	0.0%
core/src/oracle_config.rs	0	7	0.0%
core/src/cli_commands/import_pool_update.rs	0	10	0.0%
core/src/scans/generic_token_scan.rs	8	22	36.36%
core/src/main.rs	0	15	0.0%
core/src/node_interface/node_api.rs	0	18	0.0%
<!--	Total:	17	185	9.19%	-->

Files with Coverage Reduction	New Missed Lines	%
core/src/cli_commands/import_pool_update.rs	1	0%
core/src/node_interface/node_api.rs	1	0%
core/src/main.rs	2	0%
core/src/oracle_state.rs	4	0%
<!--	Total:	8		-->

Totals
Change from base Build 4593276463:	0.4%
Covered Lines:	2049
Relevant Lines:	3400

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💛 - Coveralls