adds migration for campaign changes
adds CampaignChange model
adds campaign_changes resource: belongs_to campaign
updates campaign resource to show changes
updates the campaign_changes resource index page to not show the new button
updates CampaignChange: belongs_to admin user
updates the CampaignChanges resource index
updates ability: campaign manager can read the CampaignChange resource
overrides Campaign controller PUT action to handle recording of platform changes
adds a method to the campaign model for creating the change record
change readme
Merge branch 'part3'