Improve service contract events

[renauter]

Need to catch all contract changes along the service contract flow to be able to propagate the exact struct state on clients side

• pass contract object instead of contract ID on events (not for ServiceContractCanceled())
• add events for set_metadata() and set_fees() extrinsics

Changes need to be propagated to:

• go client: Implement third party billing services events / types and calls threefoldtecharchive/substrate-client#46
• graphql: Third party billing services implementation tfchain_graphql#68

[zaelgohary]

Verified.

serviceAccountSetMetadata

serviceContractApprove

serviceContractsSetFees