Set approver of aliases/implications in BURs.

Previously only the BUR's approver was set when a BUR was approved. Set
the approver for each alias/implication in the BUR as well.

Additionally:

* Refactor `approve!` to take a user instead of just a user id.
* Be mass-assignment permissions aware when setting approver_id.

app/controllers/bulk_update_requests_controller.rb

@@ -31,7 +31,7 @@ class BulkUpdateRequestsController < ApplicationController
   end
 
   def approve
-    @bulk_update_request.approve!(CurrentUser.user.id)
+    @bulk_update_request.approve!(CurrentUser.user)
     respond_with(@bulk_update_request, :location => bulk_update_requests_path)
   end
 

app/controllers/tag_aliases_controller.rb

@@ -43,7 +43,7 @@ class TagAliasesController < ApplicationController
 
   def approve
     @tag_alias = TagAlias.find(params[:id])
-    @tag_alias.approve!(CurrentUser.user.id)
+    @tag_alias.approve!(CurrentUser.user)
     respond_with(@tag_alias, :location => tag_alias_path(@tag_alias))
   end
 

app/controllers/tag_implications_controller.rb

@@ -48,7 +48,7 @@ class TagImplicationsController < ApplicationController
 
   def approve
     @tag_implication = TagImplication.find(params[:id])
-    @tag_implication.approve!(CurrentUser.user.id)
+    @tag_implication.approve!(CurrentUser.user)
     respond_with(@tag_implication, :location => tag_implication_path(@tag_implication))
   end