[nrk] improve extraction
[nrk] improve extraction

- improve format extraction for old akamai formats
- update some of the tests
- add is_live value to entry info dict
- request instalments only when their available
- fix skole extraction

spvkgn/youtube-dl,spvkgn/youtube-dl,rg3/youtube-dl,ozburo/youtube-dl,Tatsh/youtube-dl,ozburo/youtube-dl,rg3/youtube-dl,Tatsh/youtube-dl