Support custom mapping types

[phochste]

Currently the data mapping only allows string, integer,binary,datetime but doesn't check for other types like int4, int2, bool. Make it an option to use an exact data type when speficied. E.g.

bags:
        data:
                mapping:
                    _id:
                        type: 'varchar(255)'
                        required: 1
                        index: 1
                        column: handle
                        unique: 1