Vote statistics polling on Vote step

[andreslucena]

This PR implements the polling on Admin's panel during the Vote step.

It also introduces multiple fixes that were mentioned in other reviews:

• Makes the Vocdoni API environment configurable:

Decidim::Vocdoni.configure do |config|
  config.api_endpoint_env = "stg"
end

• Infer the Explorer Vote URL from this environment
• Opens the votes verification links in a new tab
• Adds a couple more checks on the SetupForm: if there's any photo on this election and if the participatory space is published
• When the client didn't have any tokens for working with the API (after 5 Elections setup) there was a bug while calling the collectFaucetTokens method
• Adds a description while creating the Elections to explain what's Vocdoni (to be improved)
• Adds the button to publish/unpublish in the Election edit form

Screenshot

Testing

1. Set up an Election
2. Vote on it
3. Run the bin/rails decidim_vocdoni:change_election_status task so it changes the step
4. Go to the steps
5. See that you have 1 vote
6. On another tab, vote again with other participant in census
7. See that in less than 30 seconds you have the new vote on this page

[andreslucena]

This in decidim side, the command bin/rails decidim_vocdoni:change_election_status should improved, probably should be a job too. It should echo information about what elections are change the status. In my case I forgot to run this command after setting up the election, the status didn't change to "vote" (but I could vote anyway) but then it wasn't changing to the "voted_ended" status.

Yes, this is being improved on #40