Change extra heat method

[spahrenk]

Description

• Changes the method for applying extra heat. Extra heat is specified by a pointer to a std::vector when calling runOneStep. Formerly, extra heat was (vaguely) associated with a HeatSource member of a HPWH object. This PR removes this association.
• Previously, an extra-heat vector of size N specified power to the lowest N tank nodes. It now represents a full power distribution of arbitrary size across the tank height.
• These changes were tailored to match the the original method by calculating a modified, thermal distribution based on tank parameters, rather than directly using the specified distribution itself. Apparently, this reduces "swoopiness".
• No changes were made in this branch to conserve energy, which are address in a different PR.
• This branch passes all HPWH tests. It will cause failure of the cse test dhwsolar.

Author Progress Checklist:

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