This conflicts with the KDE_INSTALL_PLUGINDIR and prevent the
dolphin plugin to be installed at the right location.
Since csync no longer have plugin, this can be removed
since the entire ting is so incredibly broken in cmake,
use the approach taken by csync (which emulates the
approach of autotools), to get the directories right.
This mandates changes in the theme, which need discussion
(APPLICATION_SHORTNAME must now equal appName(), and
APPLICATION_NAME should equal appGuiName()).
