Improvements, bug fixes and tests in MySQL port; 

Test psql and mysql separately, depending on platform support. All the logic is in `test.sh`, and subtests are in `test/`.

Added a `ndbloader` for mysql cluster data loading. The functionality is in DataLoader, but it is not yet used in DeepDive pipeline.
 
Updated all unit tests and integration tests to fully support MySQL.

Added a new integration test: spouse example, only for MySQL.

Like psql `COPY table FROM 'path_to_file'`, `LOAD DATA INFILE` may not work when the client that runs `mysql` is on a different machine with the server. I just changed it to `LOAD DATA LOCAL INFILE` here and it will support reading data from client.