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

Customer can buy Virtual MAster

It creates unresolvable dependency

This reverts commit 42c90b1fce32809059cbf923f351506e4ee8c248.

Break everything, to investigate how we could integrate Open Order with Compute Node