Add I/O for ElectricHeater, ASHPWaterHeater, and ASHPSpaceHeater

[zolanaj]

Please check if the PR fulfills these requirements

• [X] CHANGELOG.md is updated
• [X] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce?

• Adds input and output models for the ElectricHeater, ASHPWaterHeater, and ASHPSpaceHeater technologies.
• Adds attributes can_serve_space_heating, can_serve_dhw, and can_serve_process_heat to input models of heating technologies and storage systems

Does this PR introduce a breaking change?

(What changes might users need to make in their application due to this PR?) None (defaults are set up so that all legacy heating technologies are capable of meeting all loads)

Other information:

Additional TODO's for this PR to be ready to merge:

• [ ] update time-series COP and capacity factor inputs after they are calculated in REopt.jl
• [ ] add tests for bad inputs to new models and process heat load