- remove the + and - buttons, and add a single install button
  instead. Current implementation of uninstall / install has a
  toggle behaviour, so having two buttons was misleading.
- add a fetch button, to load the online repository on request only,
  as done in the qt interface.

macosx/addon manager: revert xib file to the Interface Builder 3.2 format to fix compilation on jones

no fancy UI, but it works

Needs further UX improvements