* GNOME_Gnumeric.server.in.in: Add Bonobo Zoomable interface.

* src/main-component.c (control_activated_cb): Don't set
wbcc->bcontrol here.
(zoom_level_from_index, zoomable_set_zoom_level_cb,
zoomable_zoom_in_cb, zoomable_zoom_out_cb,
zoomable_zoom_to_fit_cb, zoomable_zoom_to_default_cb): New
functions to support zoomable interface.
(add_interfaces): Add zoomable interface.
(gnumeric_component_factory): Call wbcc_set_bcontrol.

* src/workbook-control-component.c (wbcc_zoom_feedback): Implement
method.

* src/workbook-control-component-priv.h (struct
_WorkbookControlComponent): Add 'zoomable' attribute.