Add Tux Paint stamps to paint

This patch add tuxpaint stamps to paint activity,
if the stamps are installed (tuxpaint-stamps package)
the option in the menu will appear.

This will show a dialog with all tuxpaint stamps, click one
and it will set at stamp in paint.
Load stamps from journal and remember it.

This patch add Load from journal icon in the Load stamp
icon view. Just click it and object chooser will appear,
choose the image, and It will set as stamp.

Also, saves the ids of the images and add the image to the store.
When you relaunch the activity, if the object exists, its added
to the store