Make vote-update reward token parameter optional

[greenhat]

Close #173 Close #219 Close #226 Close #159

Todo:

• [x] upgrade running pool to new update contract;
• [x] test new update contract(test minting new reward tokens is extracted to #229);
• [x] update UpdateContractParameters defaults in default_parameters.rs;
• [x] set new update contract hash EIP23 PR in https://github.com/ergoplatform/eips/pull/89

[coveralls]

Pull Request Test Coverage Report for Build 4312462594

• 52 of 122 (42.62%) changed or added relevant lines in 17 files are covered.
• 6 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.4%) to 61.001%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
core/src/oracle_config.rs	0	2	0.0%
core/src/box_kind/ballot_box.rs	15	18	83.33%
core/src/cli_commands/prepare_update.rs	0	5	0.0%
core/src/cli_commands/vote_update_pool.rs	2	9	22.22%
core/src/explorer_api/explorer_url.rs	0	10	0.0%
core/src/explorer_api.rs	0	11	0.0%
core/src/main.rs	0	14	0.0%
core/src/cli_commands/update_pool.rs	5	23	21.74%
<!--	Total:	52	122	42.62%	-->

Files with Coverage Reduction	New Missed Lines	%
core/src/cli_commands/update_pool.rs	1	53.96%
core/src/cli_commands/vote_update_pool.rs	1	60.71%
core/src/main.rs	1	0%
core/src/cli_commands/prepare_update.rs	3	67.05%
<!--	Total:	6		-->

Totals
Change from base Build 4144149595:	-0.4%
Covered Lines:	2035
Relevant Lines:	3336

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💛 - Coveralls