Add central water-heating systems to data model

[spahrenk]

Adds central water-heating systems to data model. Revisions to the hpwh-data-model submodule were incorporated to enable JSON specification of single- and multi-pass split systems. Effort was made to ensure that data-model initialization of these models from JSON representations reproduces results from their corresponding Preset representations.

Notes:

• A setpoint is not specified in two "testLargeComp..." test schedules. To reproduce these references, a standard_setpoint was added to the hpwh-data-model, to match that Preset output.
• The Mitsubishi QAHV_N136TAU_HPB_SP incorporates a secondary heat exchanger in the capacity calculation. A corresponding (optional) data group with the additional parameters was added to the data model.
• The "testLargeComp..." tests steps the ambient T down to 0C in 0.5C steps. The Preset polynomial performance curves for the CWHSs were sampled at each of these ambient Ts to match test references.
• Single-pass CWHSs require a grid axis for each of ambientT, heatSourceT, and outletT. HPWH assumes the outletT equals the setpointT (with an offset for the Mitsubishi model, above.) To reproduce refs, it is sufficient to add any setpointsTs used in the simulations to the outletT grid axis. The setpoint of 65C used by "testLargeCompHot" is added to the axis when maxSetpoint exceeds 65C. Furthermore, Nyle single-pass models use a reduced max setpoint below a given ambient temperature, which is also added, if needed.
• NyleCXXA_C_MP (cold-weather package) models use custom resistance-defrost map values. These are assigned via code pending identification in the data model.
• Particular interpolation/extrapolation methods are used for existing preset grid definitions. Code was added to set these methods when loading from JSON to reproduce existing test results. For new conversions from polynomial maps to grids, cubic interpolation is used for ambientT and heatSourceT axes.
• The TamScalable_SP... presets have two VIP heat sources assigned: compressor and top resistance. Although HPWH allows this, it prevents more than one resistance VIP. The hpwh-data-model currently allows identifying only a single principal_heat_source, so a hard-code fix was used to designate both heat sources as VIP.