Refactor schema validation #53
Description
Right now we use a mixture of the validator package, a default projection (on users), normal "-" and "omitempty" annotations and manual work like user.password = "".
Having good, extendable, readable validation would be great and I think we can do it using func (*Database) RunCommand to set the validation schema
Even if it doesn't solve those problems, it removes a dependency.
This might help solving #51
omitempty all json fields ?