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.
Merge pull request #86 from dkasak/quiet-flag

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