Feature: Automatically determine sample type using gene expression

[mdshw5]

• [ ] add "housekeeping genes" parameter to config.json
• [ ] add code to build "housekeeping" salmon index files for determining sample type
• [ ] add code to sequentially load these index files and quantify the first 1e6 reads
• [ ] add code to sum counts for "housekeeping" quant.sf files and determine most likely sample type composition
• [ ] add argument parser to expose new auto sample type determination

h/t @singerj