Mix of contract modifications and tests

[martinkersner]

Description

Contract-related changes

• New parameter (address refundRecipient) when requesting for service with temporary account
• Move payment in Request-Response service after cleanupAfterFulfillment (return list of oracles that should be paid)
• estimateFee made public so consumers can know how much $KLAY to send before requesting for service

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.