Combined two loops into one loop

[james-prior]

I did not create the a6ccccc commit or its log comment. The a6ccccc commit was created by someone else apparently by combining (squashing) the following commits which I did create.

• de49b64 2017-10-18 16:10:15 -0400 thermostat/core.py: calculate_epa_field_savings_metrics(): Fix bug. (origin/jp-combine-loops, jp-combine-loops) [James Prior]
• 8a92270 2017-03-09 23:04:20 -0500 thermostat/core.py: calculate_epa_field_savings_metrics(): Refactored two loops into one near end. [James Prior]
• 560224a 2017-03-09 21:43:54 -0500 thermostat/core.py: Slightly DRYer; Use generator expressions instead of list comprehensions. (origin/jp-gen-expressions, jp-gen-expressions) [James Prior]
• 5d0b55c 2017-03-09 21:38:51 -0500 thermostat/core.py: RESISTANCE_HEAT_UTILIZATION_BINS_MIN_TEMP = 0 (named a magic number, DRY) (origin/jp-dev-magic-numbers, jp-dev-magic-numbers) [James Prior]
• 80df14a 2017-03-09 21:24:53 -0500 thermostat/core.py: RESISTANCE_HEAT_UTILIZATION_BINS_MAX_TEMP = 60 (named a magic number, DRY) [James Prior]
• b0a3389 2017-03-09 21:16:39 -0500 thermostat/core.py: RESISTANCE_HEAT_UTILIZATION_BIN_TEMP_WIDTH = 5 (named a magic number, DRY) [James Prior]
• 13c927c 2017-03-01 14:13:41 -0500 docs/tutorial.rst: Added missing installation command for conda environment. (origin/jp-activate-conda, jp-activate-conda) [James Prior]