Button: Fix checked prop on button's input not always applied correctly

[hnrch02]

Fixes #14137

This fixes it properly rather than just reverting 4b40ee6.

Example: http://jsbin.com/kudav/1

BTW, the key to reproducing the problem mentioned in #14137 is to search for the point in the button where the cursor is in its default state and by that hovering over the invisible checkbox. Said checkbox can also be clicked and that's what is primarily causing these problems. This was introduced by #12794.

/cc @cvrebert @fat @Kolyunya @pixelchutes

[hnrch02]

This breaks the tests. We have three options:

1. Rewrite the tests so that they work with delay this PR currently adds.
2. Use a pure CSS fix for this by applying pointer-events: none; on the inputs, but this does only work for IE11+.
3. Rewrite the button plugin to rely on the browser to update the checked property and toggle the .active class of the labels by listening for changes on the inputs. This only works with IE9+, as change has buggy behavior in IE8.

[cvrebert]

Closing per #14137 (comment)