Clean up redundant constants with different values

[martin-mosteiro]

cea.constants includes the following constants:

# Ground/soil properties
SOIL_Cp_JkgK = 2000
"""Soil specific heat capacity in J/(kg·K). Reference: A. Kecebas et al., 2011."""
SOIL_lambda_WmK = 1.6
"""Soil thermal conductivity in W/(m·K)."""
SOIL_rho_kgm3 = 1600
"""Soil density in kg/m³."""

cea.optimization.constants includes the following:

# pipes location properties
Z0 = 1.5  # location of pipe underground in m
PSL = 1600  # density of ground in kg/m3
CSL = 1300  # heat capacity of ground in J/kg K
BSL = 1.5  # thermal conductivity of ground in W/m.K

And cea.technologies.constants includes:

NETWORK_DEPTH = 1  # m

Of course, these properties depend on the exact composition of a given soil sample and the design of the network, so differences are reasonable, but since each of these aims to represent generic "ground" or "soil" and a generic "network", then they appear to be redundant. (What's worse: A. Kecebas et al., 2011 does not seem to actually contain any reference values for soil, unless it is a different paper to the one cited elsewhere in CEA.)

Additionally, cea.demand.hotwater_loads.calc_water_temperature includes the exact same values as in cea.constants:

    heat_capacity_soil = 2000  # _[A. Kecebas et al., 2011]
    conductivity_soil = 1.6  # _[A. Kecebas et al., 2011]
    density_soil = 1600  # _[A. Kecebas et al., 2011]

The easy first fix is to use the pre-defined constants in cea.demand.hotwater_loads.calc_water_temperature and to unify the other parameters in the various constants files. But, in general, it might be necessary to go through CEA verifying where there are duplicate constants and (potentially worse) duplicate constants with different values.

[martin-mosteiro]

Note: PSL, CSL and BSL aren't used anywhere in the code so I've removed them. Z0 was used once to calculate ground temperature, so I've replaced it with NETWORK_DEPTH for consistency.