added service api facade

added comments in client facade noting functions that should be moved to
the service facade

added service api client
fixed review comments
more fixes from reviews
bump service facade version
Merge pull request #1252 from mattyw/add-metric-credentials-api

Added service api facade

Added a service facade to the api. Current only implements setting metric credentials. Eventually service specific calls from the client should be moved here

(Review request: http://reviews.vapour.ws/r/563/)