Refactor save config

[GlottalTrill]

Mostly linting config.go and getting myself familiar with the code base. Improving how configuration variables are used will make it easier to compartmentalize the other functions into internal modules.

• Adds comments on variables for future Godoc support
• Adds basic test on saveConfig
• Moves setting of defaults to configInit
• Removes unused function saveTempFile

I generated a few contact sheets but I don't have a comprehensive test suite. That might be the next thing I work on.