Added repo and reposervice files for PerformanceIndicatorSpecification, implemented Service methods.

Tmf 674 feature

See merge request !24

Merge branch '24-introduce-a-check-in-service-order-posting-for-the-requested-service-specification' into 'develop'

Implemented check for existence of Service Specifications for a Service Order

See merge request !22

Resolve "Update Service Order with Expected Completion Date"

See merge request !23

Update Supporting Services' end date upon Service Order Expected Completion Date update

See merge request !21

Resolve "Increase test coverage in TMF638"

See merge request !18