Submerge 3.4.5

- Support for HEVC (High Efficiency Video Coding or H.265) export compatible with iOS 11, tvOS 11 and macOS High Sierra.
- FFmpeg updated to the 3.3.3 "Hilbert" release.
- The exported file now has the subtitle language code as part of it's file extension. Like mymovie.eng.mov.
- Now supports WebVTT time codes in the 00.00.000 form.
- Various bug fixes and tweaks.