Page Label handling, other fixes

Added the function to handle links from the toolbar, also added functions to disconnect all ev-view handlers once it has been replaced by ev-web-view, and vice-versa(to drop all handler associated to ev-web-view).

Also the unref call to job_thumb was causing thumbnail jobs to crash with GTK2, so had to revert that, now we're back to the document folder not getting deleted from disk.