OrionMongoSink

[frbattid]

OrionMongoSink will be in charge of persisting Orion context data in a historic fashion within a MongoDB deployment.

The way this sink will build the historics will be very similar to the already existent OrionHDFSSink, OrionMySQLSink and OrionCKANSink, i.e. by appending ("to append" has several means, deppending on the final backend) new raw data to the already existent one.

Because raw data is stored, this sinks differentiates from OrionSTHSink (issue #19), which is in charge of updating already exitent data with new notified data since the goal is to offer aggregated measures to the end user. Nevertheless, in the future most probably the usage of the Mongo Aggregation Framework will allow us to generate such aggregated measures based on the stored raw data; in that case the usage of OrionSTHSink becomes deprecated (? --> @gtorodelvalle).

[frbattid]

Implemented in PR #366