Added mongodb as requirement.
Updated bower packages configuration.
Added mongodb library and updated database instantion code to manage the used database (tingodb or mongodb).
Added singleton object to manage identities. It is able to generate a BSON compatible _id for mongo or standard _id for tingo starting from a generic id.
Updated dataset plugin data retrieve/insertion/update calls to used the new identity system.
Updated peer plugin data retrieve/insertion/update calls to use the new identity system.
Updated reference plugin data retrieve/insertion/update calls to use the new identity system.
Updated repository plugin data retrieve/insertion/update calls to use the new identity system.
Updated setting plugin data retrieve/insertion/update calls to use the new identity system.
Updated system plugin data retrieve/insertion/update calls to use the new identity system.
Updated tag plugin data retrieve/insertion/update calls to use the new identity system.
Updated user plugin data retrieve/insertion/update calls to use the new identity system.
Added fields from mongo configuration into the settings panel.
Merge origin/master