Refactor concept of current budget

When there was only one budget this implementation worked fine

Nowadays there can be multiple budgets, and therefore the definition of
the current_budget has changed. It is no longer a budget that has not
finished, but rather, the last budget created that is not in the
initial drafting phase.

Budgets in the drafting phase are not considered the current_budget,
but rather a budget that is still being prepared and that soon will
become the current_budget

app/models/budget.rb

@@ -31,7 +31,9 @@ class Budget < ActiveRecord::Base
   scope :reviewing_ballots, -> { where(phase: "reviewing_ballots") }
   scope :finished, -> { where(phase: "finished") }
 
-  scope :current, -> { where.not(phase: "finished") }
+  def self.current
+    where.not(phase: "drafting").last
+  end
 
   def description
     send("description_#{phase}").try(:html_safe)
@@ -93,10 +95,6 @@ class Budget < ActiveRecord::Base
     balloting_process? || finished?
   end
 
-  def current?
-    !finished?
-  end
-
   def heading_price(heading)
     heading_ids.include?(heading.id) ? heading.price : -1
   end