hls: Add support for next/prev track

Fixes #2145
hls: Remove dead code
js: Also repair broken UTF-8 when using HTML meta tags to deduce encoding

Fixes #2147
media: Bump epoch when we flush media queue
glw: Fix missing relayout trig when container constraints changes

Caused problem when in conditional ui rendering mode

Fixes #2115
js: Treat charset=UTF8 as UTF-8