refactor: find a way to share common code between checkable components

[robertmesserle]

As is, there is a lot of copy/pasted code shared between radio buttons, checkboxes, and toggle buttons. We need to look into a way to rely on shared code rather than duplicate code.

[devversion]

I think that relates to #598 as well.

[shlomiassaf]

If done, also consider #347 in the process.

[jelbourn]

Exploring new mixins in TypeScript 2.2.

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