Add support for nested repeated tasks

[shalinshah1993]

From @shalinshah1993 on July 12, 2018 18:51

Currently, if an SED-ML file contains nested repeated tasks, simulation library will throw a warning Warning! Nested repeated task found and ignored!

At some point, this feature needs to be added to the simulation library. This issues thread serves as a discussion point.

Copied from original issue: shalinshah1993/SBSCL#55