Add missing post route for dashboard widget move

This is to fix the following error:

ActionController::RoutingError (No route matches [POST]
"/report/db_widget_dd_done")
...

https://bugzilla.redhat.com/show_bug.cgi?id=1167308
Merge pull request #1119 from mzazrivec/fix_widget_move_routing

Add missing post route for dashboard widget move