always rescan synonyms on launch
make QSDownloads available for use in plug-ins
forget past modifiers when switching applications

fixes #1713
remove redundant code to hide the interface

…when switching applications. QSInterfaceController already takes care
of this in a cleaner way.
Merge pull request #1715 from quicksilver/i1713

fix a small bug with modifier-only activation
Merge pull request #1714 from quicksilver/rob/fixes

small fixes from a dead pull request