Don't use tick for elapse time.

Closes #5.

* src/dctc/java/com/dataiku/dctc/display/AbstractTransferRateDisplay.java: Implementation
* src/dctc/java/com/dataiku/dctc/display/LessSimpleDisplay.java: Adjust.
Correct message display.

Closes #23.

* src/dctc/java/com/dataiku/dctc/display/AbstractTransferRateDisplay.java,
  src/dctc/java/com/dataiku/dctc/display/AbstractThreadedDisplay.java: Here