Update the Ethereum bridge specs

[sug0]

• Ethbridge specs #99
• Update description of voting on eth events across epochs (algo was changed)
• Describe NUTs
• Describe new whitelisting mechanism
• Describe how wNAM gets minted on the contracts
• Update governance contract description (probably outdated)
• Describe how we cap wNAM on Namada
  • Keep track of wNAM tokens that have been minted on Ethereum namada#1722