add a metamodel defined tag to the default data base name; exclude the parameter WorkingDir from the database

new option menu for solvers (much simpler than in gear menu); needs to be enhanced with other actions

this amkes it easier to ship bundles (e.g. gmsh+getdp)

(this allows to aggregate many tree rebuilds into a single one, thus decreasing the gui overhead for codes sending many refresh requests)

when opening solver files (through file->open or e.g. in the finder) we now perform onelab_cb(reset); I think this is the right(TM) thing to do

Warning: this can potentially break stuff :-)

will wait until after I come back to integrate his changes

fix crash (when deleting widget with focus and pending callback; make sure the tree gets the focus before we delete all the children)