Make vote-update reward token parameter optional

[greenhat]

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

Todo:

• upgrade running pool to new update contract;
• test new update contract(test minting new reward tokens is extracted to Test minting new reward tokens #229);
• update UpdateContractParameters defaults in default_parameters.rs;
• set new update contract hash EIP23 PR in [EIP-0023] In update contract check reward tokens are either preserved or voted by ballot boxes eips#89

[coveralls]

Pull Request Test Coverage Report for Build 4184184037

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 49 of 101 (48.51%) changed or added relevant lines in 14 files are covered.
• 201 unchanged lines in 13 files lost coverage.
• Overall coverage decreased (-0.2%) to 61.227%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
core/src/contracts/update.rs	2	3	66.67%
core/src/cli_commands/prepare_update.rs	0	2	0.0%
core/src/box_kind/ballot_box.rs	15	18	83.33%
core/src/cli_commands/vote_update_pool.rs	2	9	22.22%
core/src/explorer_api.rs	0	12	0.0%
core/src/main.rs	0	12	0.0%
core/src/cli_commands/update_pool.rs	5	20	25.0%

Files with Coverage Reduction	New Missed Lines	%
core/src/cli_commands/vote_update_pool.rs	1	60.71%
core/src/contracts/oracle.rs	1	87.1%
core/src/pool_commands/test_utils.rs	2	93.94%
core/src/cli_commands.rs	6	0.0%
core/src/contracts/update.rs	6	81.82%
core/src/contracts/pool.rs	8	84.93%
core/src/cli_commands/prepare_update.rs	9	67.05%
core/src/contracts/ballot.rs	12	80.61%
core/src/explorer_api.rs	17	0.0%
core/src/contracts/refresh.rs	18	75.38%

Totals
Change from base Build 4144149595:	-0.2%
Covered Lines:	2026
Relevant Lines:	3309

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💛 - Coveralls