cache scopes

[its-danny]

config file needs to change to accept a scopes array. on first run (with --autocomplete), save the found scopes to the config via appending it. this allows the user to set up their own list when starting a fresh repo, while also populating it with new ones. every time you commit with koji, the list should be updated.

for this to work, commit_types needs to work differently. when we load a config, we need to check for commit_types and use the default if they don't exist. currently we only use the default if a config file doesn't exist at all.

this sounds like the correct thing to do, but i'm no totally sure it's necessary. autocomplete is an optional flag, and in a large repo it only slows startup down by milliseconds.