Update code for Shadow DOM V1 spec

[mliszcz]

• use element.attachShadow instead of deprecated createShadowRot (all components affected)
• use slot instead of content insertion point (button affected)

This issue is blocked until these features are implemented in both FF and Chrome.

[mliszcz]

https://github.com/w3c/webcomponents/blob/gh-pages/proposals/shadow-dom-v1-in-blink.md#unified-distribution https://bugs.chromium.org/p/chromium/issues/detail?id=531990 https://bugzilla.mozilla.org/show_bug.cgi?id=1205323