Don't reparse logs and pre-parse full log

[equationcrunchor]

Code written; needs tests.

[rhuffy]

This involves two steps.

1. On the cloud functions side, after a new .csv file is created and saved to Cloud Storage, save the filename to Firestore.

2. On the frontend, before calling the cloud function, check to see if there already exists a filename on Firestore for this file with this combination of columns and log rate. If yes, get a download link for that file. Else, proceed as normal and call the cloud function.

[rhuffy]

For log file cache keys, a good format would be <Column A>,<Column B>,<Column C>,<Log Rate>. Column names should be alphabetized.