Bibarchive: Exception handling for DB API

* InvenioBibArchiveError used instead of returning False for
exceptions
Bibarchive: Regression Tests Updated

* Tests now handle DB API using error messages
Bibarchive: Basic Archiver file

* Pass recid and version to create a new compressed bagit and
entry in the mongodb
Bibarchive: Config variables for DB API

* DB API now uses config variables for mongo server hostname and
port, database name and collection name.
Bibarchive: Final code cleaning

* Archiver uses invenio error

* Record IDs are passed as strings instad of int's

* General cleaning
Bibarchive: Final comments

* Final comments added