Add -q, --quiet flag for some operations.

This adds a quiet flag (and setting) for some operations, namely AUR search and view dependencies. This is useful when parsing Aura's output in scripts since it outputs only package names, stripped of colour. The same setting could be used for new features in the future, if need arises.

Feel free to change any part of the implementation you don't like. I wasn't too sure with all the flag/option code; what is the semantic difference between a dual flag and a hijacked flag?

I made this a setting since it seemed like a useful thing to have for possible future operations. I've looked through the existing options but I didn't notice any other place where quiet would make sense.

Also, with -q, -Ad now outputs AUR and pacman dependencies as one long list. On one hand, this is a good thing because it will make the output compatible with more Unix tools out of the box. On the other, it limits the usefulness for more complex scripts since they have no way of telling what's a repo package and what's an AUR package. Perhaps it should still prefix the packages with `<repo>/`?