add charge_for column to price_policies table

Pricing model changes (Task #73569)
validate charge_for and store values in constant

Pricing model changes (Task #73569)
revise UI

Pricing model changes (Task #73569)
switch old price policy for new

Pricing model changes (Task #73569)
fix specs
update for new PP
add charge_for column to price_policies table

Pricing model changes (Task #73569)
validate charge_for and store values in constant

Pricing model changes (Task #73569)
revise UI

Pricing model changes (Task #73569)
switch old price policy for new

Pricing model changes (Task #73569)
fix specs
update for new PP
add #discount_for
default usage_mins to 60
enable new estimation calculation; always save usage mins as 60; ensure other *_mins attributes are nil

Pricing model changes (Task #73569)
rename old calculations module

Pricing model changes (Task #73569)
split estimation and calculation methods into their own module

Pricing model changes (Task #73569)
Merge remote-tracking branch 'origin/simple_pricing_73569' into simple_pricing_73569

Conflicts:
	app/models/instrument_price_policy.rb
	app/models/instrument_price_policy_calculations.rb
	app/models/old_instrument_price_policy.rb
	spec/models/instrument_price_policy_spec.rb
we don't want to use #usage_mins

Pricing model changes (Task #73569)
add #rate_per_minute and #subsidy_per_minute

Pricing model changes (Task #73569)