fix english settings label regarding how to view videos

Quickfix (suggestion) for the weird settings label

Play videos directly in the media viewer

which does precisely the opposite of what you (/I) would expect. My replacement suggestion is

Play videos in a popup frame

which seems to be what it actually does (in user-understandable words).

@hj This is my first (very tiny) attempt at contributing to pleroma.

merged

mentioned in commit 59f29313