Implement display of row_number parameter for child tasks

[RaduCStefanescu]

One of the features necessary for displaying child tasks is to display the row number that the child task needs to transcribe. This should be implemented when we have PyBossa integrated in the dev environment.

There are a few changes necessary to achieve this functionality:

• all current child tasks need to be modified to accept the row_count parameter
• all current templates need to display the row_count parameter

[cnstlungu]

I'd like to help out here - taking this task on.