Use <Icon.Text> in place of <Icon text> prop

[kennethnym]

As suggested here. Personally I think it makes more sense since it's a wrapper component rather than an "addon" that acts as a modifier of the base class, i.e. instead of adding to the base icon class like icon icon-text, it replaces the icon class.

Example:

<Icon.Text>
  <Icon>...</Icon>
  <span>label</span>
</Icon.Text>

cc @couds

[kennethnym]

This is added in #339