Comments

[jschr]

This PR add comments functionality per this design spec: https://github.com/KristerV/heliumpay-budgetweb-backend/issues/24

Tasks

• [x] Create new comment
• [x] Update existing comment
• [x] Vote on comment
• [x] Delete comment (soft delete)
• [x] Get all comments for a proposal
• [x] Prevent voting on own comments
• [x] Return masked deleted comments when retrieving proposal comment threads
• [x] Tests for all added endpoints
• [x] Update readme

New API Endpoints

GET   v0/comments?proposalHash=         // Get all comments for a proposal
POST  v0/comments                       // Create a new comment
PUT   v0/comments/:id                   // Update a comment by id
DEL   v0/comments/:id                   // Delete a comment by id
POST  v0/comments/:id/vote              // Vote on a comment