Properly remove event listeners from container element (fixes #710).
Properly remove event listeners from container element (fixes #710).

For three event listeners added to the container elements weren't being
removed properly, since `removeEventListener` was mistakenly being called on
`uiContainer` instead. This was preventing garbage collection.

mpetroff/pannellum,mpetroff/pannellum,mpetroff/pannellum,mpetroff/pannellum