Add option to disable building proxies upon adding movie clips

When adding a movie clip, a "BL_proxy" folder is immediately created to generate proxies. However, there are many times where I'm only doing a temporary, quick edit, and the clips are low-quality enough that building proxies are unnecessary. Building proxies also adds a lot of processing upon adding the clip, which slows things down and makes it harder to click the "Cancel" button for building proxies.

Proxies are set to be generated every time a movie clip is added, with no visible option to disabling it.

Please add an option to disable proxies from being generated with every clip added, especially since performance is at a point where they're not always necessary.