Basic Mongo implementation

[pacoVela]

No description provided.

[stof]

this makes it impossible to use several mongo handlers at the same time as the second one would replace the mongo client.

[stof]

There is 1 missing check in the Configuration class: checking that $config['mongo'] is set when selectionmongo`` as type.

[Seldaek]

Alright, looking good now I think. Thanks!