Force speed but not for music

[samyk]

Adds an option under Player->Forced Playback Speed (when enabled) to Force playback speed for music, defaults off so that if user does force an alternate playback speed, it doesn't apply to music.

Improved the music detection by checking the description (and in some cases the description doesn't load, so interval runs until it exists but maxes out at 5 secs)

I don't know the other languages so I used English in all the locale files for consistency.

Resolves #1538

[ImprovedTube]

English in all the locale files for consistency

(We made a locale.py for this before https://github.com/code-for-charity/ImprovedTube-for-YouTube/blob/master/py/locale.py )

Can also skip the step for now like: text: 'Force playback speed for music', since extensions default to displaying that. - (that's as long as it is not translated, once translated it unfortunately only allows letters numbers & underscores 😆 & these wont be displayed in Firefox)

[samyk]

Ahh nice! Might be neat to not update the locales at all, and instead have locale priorities that gets generated when the plugin is loaded. So if someone adds something to the en locale, it should not exist in any others (and that makes it easier for people to know what needs to be translated). Instead module loads, goes through all locales to produce object of each key, and fills it out based on language priority, so if someone's priorities are 'it->es->en->all others' then it first looks for key in it and if not there, then looks in es, etc. Would only happen on startup so runtime is fast.

[ImprovedTube]

when the plugin is loaded.

( *at installation/updates and held in storage; leaving the way predefined by the browsers)

[samyk]

when the plugin is loaded.

( *at installation and held in storage, leaving the way predefined by the browsers)

even better!