comments: Allow retrieving all comment votes.

[lukebp]

The comment votes endpoint currently only allows you to retrieve comment votes for a specific user ID. This initial implementation was restrictive because that was all that politeiagui needs. Opening up the endpoint to allow a client to retrieve all comment votes made on a proposal, without needing to provide a user ID, has been requested in order to help analyze the proposal process. Comment votes are already public, so there is no reason to not allow this.

// Votes returns the comment votes that meet the provided filtering criteria.
type Votes struct {
	Token  string `json:"token"`
	UserID string `json:"userid"`
}

Implemenation

• The user ID field needs to be made an optional filtering criteria.
• The returned votes need to be paginated. A page number field neeeds to be added to the request payload. This should default to page 1 if not provided.
• The page size should be added to the policy reply.
• The comments plugin command needs to be updated to reflect the new implemenation. The page number and the filtering criteria (optional user ID) need to be applied.
• Update pictl.

This should be done in a backwards comptable manner. Breaking changes to public API are not allowed.