Add 'self.message' to the Torrent class

this 'message' attribute will allow pyrt to determine if the status of
the torrent is 'Error' or not, if this message attribute is empty string
then there's no errors, if there's a tracker 'message', there's an error
check if the status is 'Error'

in the 'getState' method, I added a new status 'Error' and a new test
for that.
Added 'Tracker Status' to th dropDown table

taking advantage of the new 'message' attribute.
Added a new method 'getTrackerMessage'

this method is used to display the tracker status in the dropDown table.
Added 'tracker_message' to 'jsonObject'

so we can pass the status of the tracker to 'dropDownHTML.tmpl'