Fix migration name
Migrate backers to contributions on postgres views
Add migration to migrate user_total view to use contributions
Add migration to change notifications template name
Rename backer reports to contribution reports
Rename backer_reports_for_project_owners view to contribution_reports_for_project_owners
Rename backers_by_periods view to contributions_by_periods
Adjust down migrations to use contributions table instead of backers
Remove unnecessary migration