Non negative rate of change (ready)

* Add interval to diff quotient (day, hour) minute, second) to calculate late say transfer (KB/hour, KB/s, KB/day etc)

* Add sources option to graphbuilder create (this was required since rate of change is a derived source and if we don't want to plot both rate of change and original data)

* Add an actual network example showing use of both diff quotient (rate of change) and applying a negative filter band. (This involves loading real json data -- this could be moved elsewhere)

Also, we could rename diffQuotient selection method to rateOfChange instead (reach isn't using this yet so it's safe to make the change now).

DiffQuotient without filter:

![Without Filter](https://6ba3e55da481c78542d2-3db83ef2055a625963844ece9e36fa2a.ssl.cf1.rackcdn.com/RoCWithoutFilter.png)

DiffQuotient with filter:

![With Filter](https://6ba3e55da481c78542d2-3db83ef2055a625963844ece9e36fa2a.ssl.cf1.rackcdn.com/RoCWithFilter.png)