migrate the depreciation studies out of excel sheet -> CSV for easier multi-person editing/adding

[cmgosnell]

The depreciation studies we've compiled are currently in this spreadsheet. It houses both the raw studies and the link between those studies and the EIA plant parts. This was mostly fine when it was mostly only me adding to it, but if we have multiple people adding studies, these stages should be separated and converted to CSVs for easier diffing and merging.

to do

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1. Extract Depreciation Studies Raw tab out of deprish_raw.xlsx
2. create new CSV in inputs (perhaps deprish_raw.csv
3. Convert any pointers to Depreciation Studies Raw to deprish_raw.csv
4. Rename renaming tabs in deprish_raw.xlsx -> deprish_eia.xlsx
5. Consider if EIA to depreciation matches can be extracted into CSV as well)

More notes in #169.