Dispenser can place/recover chemical fluid. And fix an unchecked class cast.

Signed-off-by: yushijinhun <yushijinhun@gmail.com>
Fix cannot recover element fluid with empty element.

Signed-off-by: yushijinhun <yushijinhun@gmail.com>
Fix cannot recover water.

Signed-off-by: yushijinhun <yushijinhun@gmail.com>
Fix flowing fluid can be collected.

Signed-off-by: yushijinhun <yushijinhun@gmail.com>
Merge pull request #205 from yushijinhun/feature-liquid-dispenser

Dispenser can place/recover chemical fluid