[RFC-191]: Add governance proposal-quorum flag

[goran-ethernal]

Description

Added a new flag to genesis command: --proposal-quorum which defines a percentage of total stake needed for a governance proposal to be accepted. Since only validators are allowed to vote for a proposal, total stake at the moment of proposal submission will be used for quorum calculation of a given proposal.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually