added :patrons_can_renew to app configs (modified)

Conflicts:
	app/models/app_config.rb
	app/views/app_configs/_form.erb
updated ability.rb with patron renewal option
updated reservation show page based on renewal ability
made items with zero-length max renewal ineligible for renewal (modified)

Conflicts:
	app/models/reservation.rb
Renamed configuration parameter to enable_renewals (modified)

Conflicts:
	app/views/app_configs/_form.erb
broadened restrictions to all roles except superuse
add enable_renewals to strong params
updated schema