Fixed Browser Action Toggle

The browser action poorly managed state previously by just setting a false variable and toggeling, but sometimes the js execution environment would reset and the button icon would be off by one.  There's no way to check the state of the button explicitly.  Instead, the program now toggles the icon text between 'Link Finder' (default) and 'Clear Links' (once clicked).  It can use this by checking the title state and set the button appropriately.