Add text style support to SimpleTextDisplayer

[joeyparrish]

We are not currently extracting style information from subtitle formats. We also do not manipulate CSS from the default text displayer.

We could extract this information into shaka.text.Cue and pass it to the text displayer. The default displayer could then programatically style ::cue to set the appropriate properties.

[ismena]

We do extract some style info. Shaka Cue has background color, color, font weight, family, style and size properties as well as line height and wrap option.

Currently our default text displayer doesn't use this info, so we can certainly work on that.

[joeyparrish]

I stand corrected. Thanks!

[toschlog]

Yes, yes, please add this!

[avelad]

We already support <b>, <i>, <u> tags and colors.

We are closing this issue, if anyone is interested in supporting more styles, please open an issue with the specific details.

Thanks!