Prefill title of a source when prediction is added from source overview

1. User searches for a source, like http://www.dystopiatracker.com/E?t=Ella%20Minnow%20Pea
2. User clicks button: Add a prediction

Now: User has to enter title and type of the source again
Better: Type and title of the source is already prefilled in the form

needed for this
a) add source to url when button "add prediction" is clicked
b) read source from url and prefill form
