Issue639 actuator travel part 1

[dhblum]

This is for #639. It is only part 1 of what's needed to finalize the actuator travel KPI. This PR:

• Specifies the actuator travel KPI in the design documentation
• Updates the parser.py to read new actuator KPI and type tags from the read signal exchange blocks and add the new signal types to the kpis.json
• Updates the kpi_calculator.py to calculate the actuator travel KPI using the new signal types in the kpis.json.

The final implementation will need at least two additional PRs:

1. A PR to the Modelica IBPSA Library to update the read signal exchange blocks with new actuator tags for KPI and actuator type.
2. A PR to this repo to update all the test cases with the new signal exchange blocks for actuator travel KPI calculation, and to create corresponding new unit test reference results.