[OrionMongoSink, OrionSTHSink] Use MongoDB specific character set

[frbattid]

Currently, Cygnus' STH sink encodes the information used for building persistence element names. i.e. MongoDB databases and collections, by means of a general encoding function:

Every character except for alphanumercis, dots and hyphens, must be encoded as an underscore.

Such a encoding function is too restrictive for MongoDB, which accepts a wider set of characters, having a reduced set of forbiden characters, specifically these ones for databases:

/. "$

And these ones for collections:

$.
(in addition, an empty string, e.g. "", the null character and a collection begining with the "system." prefix is not allowed)

(despite the dot is not officialy accepted, we have tested in STH it works...)

(ref: https://docs.mongodb.org/manual/reference/limits/#naming-restrictions)

Regarding STH/MongoDB, Cygnus must use specific encoding functions (one for databases and another one for collections) based on the above character sets instead of the general encoding function.

[frbattid]

This must be done on current develop branch and in release/0.13.0 branch.

[frbattid]

Implemented in PR #902

It is under study if this issue will be mered into release/0.13.0. So closing, and re-opening if needed.