Feature webpack legacy

[dsilhavy]

This addresses #3619

[dsilhavy]

@bbert @mlasak I used https://github.com/stefanpenner/es6-promise here to polyfill promises. From my understanding the library automatically detects whether native promises are supported and polyfills accordingly. With that build playback im IE11 works for me.

What do you think?

[mlasak]

Correct me pls if i'm wrong but i would expect a good polyfill to use the native Promise if present and not just overwriting global one. Maybe it needs to be initialized in a different way ?

If run in chrome with Promises available i see:

[mlasak]

@dsilhavy please check my change if it still works for you as expected for legacy.

As well i think es-promise must be real dependency not only dev. Changed this, too.

[bbert]

@dsilhavy @mlasak so you took the option to include the promise polyfill in output bundle?

[dsilhavy]

@bbert Yes, I tested and promises were the only thing missing for IE11. We can consider adding separate builds once we see other platforms with additional missing dependencies. I did not want to create a separate build only for promises.

[mlasak]

@bbert the dash.mediaplayer.min.js bundle is increased by 5 kB (less than 1% increase in byte size of this file). It seams acceptable to me. wdyt?