Merge branch 'BHE' into 'master'

ProcessLib/HeatTransportBHE/BHE/BHE_1U.cpp

...arabolic/T/3D_3BHEs_array/3bhes_1U_ts_10_t_600.000000.vtu

..._BHE_GW_advection/BHE_GW_advection_ts_10_t_500.000000.vtu

...c/T/3D_Beier_sandbox/beier_sandbox_ts_10_t_600.000000.vtu

..._sandbox/fixed_power_constant_flow_ts_10_t_600.000000.vtu

...sport-bhe/3D_3BHEs_array_figures/Heat_extraction_rate.png

...D_3BHEs_array_figures/Heat_extraction_rate_closedloop.png

...3D_3BHEs_array_figures/Inflow_and_outflow_temperature.png

..._3BHEs_array_figures/Inflow_temperature_and_flow_rate.png

...transport-bhe/3D_3BHEs_array_figures/Soil_temperature.png