issue #43: sharded DBUtils
issue #43: fixed a bug related to aggregation on strings
issue #43: added tests for more operations
issue #43: fixed a broken commit
issue #43: removing variant tables on shards when the project is removed
issue #43: sharded removal of references
issue #43: addedcode for file manipulation
issue #43: sharded import of TSV files, fixed several bugs related to export/import
issue #43: extended tests for write operations
issue #43: fixed bug when DBUtils were using the wrong table
issue #43: fixed empty database/table handling
issue #43: added code responsible for dynamic class generating and mapping change
issue #43: added tests for dynamic class generating
issue #43: modified sharded methods to regenerate mapping and dynamic variant class when schema changes