Refactor HTML for apps

[muffinresearch]

Fixes mozilla/addons#9568
Fixes mozilla/addons#9563
Fixes mozilla/addons#9562

• Moves to using JSX for the HTML

TODO: As a follow-up will need to wrap the search code when login is required in the App component so that it gets the App title.

[coveralls]

Coverage remained the same at 100.0% when pulling 188eb5c on muffinresearch:better-html into e50f50b on mozilla:master.

[mstriemer]

I don't think we need to turn this off. I think it's a good rule.

[muffinresearch]

Yeah it's ok some of the time - other times I feel like it's annoying if the lack of braces and a return obscures the readability. I feel like this is one where being opionated gets in the way and I'd rather devs decide what makes sense on a case by case basis.

The reason for disabling it was because it can't deal with the abiguity of returning an object since braces and the start of the object are both { - but I'll check and see if there's extra options to deal with this case before removing it entirely.

[mstriemer]

For the object case you need to wrap it in parens. It seems a little strange but I don't think it looks too bad.

const getConfig = () => ({
  some: 'config',
});

[mstriemer]

Thanks for cleaning this up! Looks good.

r+wc

[coveralls]

Coverage remained the same at 100.0% when pulling 23c12ff on muffinresearch:better-html into e50f50b on mozilla:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 3455444 on muffinresearch:better-html into e50f50b on mozilla:master.