Fix bug 1109289

The only problem with this change is that if an event has a vidly_template but not a vidlysubmission things can go wrong but I don't know if such situation is possible
We need to change this variable name. That template `event.html` has a lot going on and it's best to stick to more descriptive variable names otherwise it might one day become hard to debug what's going on. Other things might be HD too, like the poster thumbnail for example. 
Perhaps it's as simple as calling it `vidly_hd` instead?