It was only used on OS X and couldn't be used by the FinderSync
extension since that one runs in a sandbox. So use the same system
to load images in the legacy extension by shipping them in the
extension bundle instead of the owncloud.app bundle.
This is also given that the legacy extension needs padded icons
while the FinderSync one needs unpadded icons.
This uses the new official API to show overlay icons and add our
custom context menu entry instead of hooking directly into the
Finder process and intercept drawind routines.
A dummy desktopclient target is also in the project to allow debugging
directly in Xcode while the official client can be started from the
command line. Otherwise Xcode won't allow attaching to the debugee.
Dummy icon files have been added while we get proper icon produced.
We can't use the old icons since what we use for the legacy shell
integration is already padded according to where the badge should
appear on the full icon.
