Improve performance of budget stats

[voodoorai2000]

Context

To view budget stats (admin/stats/budgets) a rake task is executed every half an hour

What

Make queries to calculate budget stats for the support and balloting phases more efficient to avoid having to use the rake task

How

• Create a large set of data using Madrid's numbers as a reference:
  40.000 participants casting 400.000 votes
• Make the page load in a reasonable amount of time 5-20 seconds
• Cache partial result variables

[raul-fuentes]

I'll do this one