remove adhoc repo_vector_t extraction from the database

[carmenfan]

there are a lot of repo_vector_t values being stored in the database, which is essentially in the form of an array with 3 values, but we also retreive them back and use them as repo_vector_t

extend repoBSON to support the storing and getting of repo_vector_t from RepoBSONs so we are not writing some adhoc 1x3 array to achieve 3 values from an embedded bson everywhere.