Use only either sector or sector_ald

[jdhoffa]

There are two "sector defining columns" in the match_result input: sector and sector_ald.

1. sector comes from the loanbook specification
2. sector_ald comes from the asset-level data

In the analysis, we should only ever use the actual data in the sector_ald column. From what I can tell, this is already happening, however, internally, we are joining and renaming and abusing the word sector when we mean sector_ald.

I think we should decide on a consistent method, so that we don't confuse people (and ourselves).
Options:

1. Drop sector as soon as data is input, and rename sector = sector_ald
2. Try to keep track of sector_ald and not accidentally reference the wrong column