Enhance the history database: record at the triple level

[jmvanel]

Currently, the metadata (author and timestamp) are not at the triple level, but are attached at the level of the pair subject - predicate.
As a consequence, in muti-value case, all triples for pair subject - predicate are labeled like the last modification, even the triples coming from Internet.

[jmvanel]

Actually the history database actually records metadata (user, timestamp) at the triple level.

The faulty code that confuses all timestamp and user information for a couple (subject, property) is
UserTraceability. addUserInfoOnTriples()
where
val resultsUser = mutable.Map[String,String]()
should be turned into something like:
val resultsUser = mutable.Map[(String,String), String]()

and probably also later change return type of
TimeSeries. getMetadataAboutSubject()
to return a List of Map's from (property, object) to (timestamp, user)
which is exactly what callers need.