v3.3.4 - Better format and resolution support

Fixed a bug where many videos were never detected and could not be
downloaded: files served from /preview/ paths were wrongly treated as
thumbnails and skipped, so the best quality was often the one missing.

• Real video files are no longer discarded for having "preview" in the path
• Direct download links (<a download>) are now detected
• All media on the page is found, not only what is scrolled into view
• AVI, MKV, FLV, MOV, 3GP, WMV, VOB and more recognised, not just MP4/WEBM
• The list is no longer truncated to three items
• Fixed corrupted translation files that could stop the extension loading

Preview depends on browser codec support: MP4/WebM play in-app, formats like
AVI or MKV download fine but cannot be previewed.