slapos_cloud: only propagate Instance Tree parameters to the Software/Slave Instance only if an Open Sale Order exists

 allow users to create Compute Node / Instance Tree

slapos_accounting: do not aply trade condition if source/destination projects are different from order

slapos_subscription_request: forbid Subscription Request which could generate Invoice with a 0 price

It leads to always return nothing, as it does a join to the category table