Separates Petitions form out into a partial
Creates PetitionsController#edit and #update as well as Petition edit view
Adds conditional in Petition show view to show or hide edit link
Creates PetitionsController#destroy
Changes flash[:notices] in destroy to display destroyed petition title instead of object hash
Creates Delete petition button on Petition show page
Updates Petitions-, Users-, and SessionsController
Adds ApplicationController#require_not_logged_in and adds before_filter to SessionsController#new, and -#create
Adds a filter to disallow people other than petition creators to edit petitions.
Adds PetitionSignature model and table