Added job attributes, fixed seeds.rb

Added some attributes like status_changed_at. Refactored migration
files.
Changes to the migration file makes it necessary to reimport the
database: db:drop, db:create, db:migrate, db:seed

app/controllers/jobs_controller.rb

@@ -3,7 +3,7 @@ class JobsController < ApplicationController
 
   # GET /jobs or /jobs.json
   def index
-    @jobs = Job.current_jobs_of_today
+    @jobs = Job.currently_working_on
   end
 
   # GET /jobs/1 or /jobs/1.json
@@ -23,7 +23,7 @@ class JobsController < ApplicationController
 
     respond_to do |format|
       if @job.save
-        format.html { redirect_to jobs_url(Job.current_jobs_of_today), notice: 'Job was successfully created.' }
+        format.html { redirect_to jobs_url(Job.currently_working_on), notice: 'Job was successfully created.' }
         format.json { render :show, status: :created, location: @job }
       else
         format.html { render :new, status: :unprocessable_entity }