Button custom colors

More contextual button colors diversify their place of application.

Example

<!-- Source -->
<button class="btn btn-black" type="button">Black</button>
<button class="btn btn-indigo" type="button">Indigo</button>
<button class="btn btn-orange" type="button">Orange</button>
<button class="btn btn-pink" type="button">Pink</button>
<button class="btn btn-purple" type="button">Purple</button>
<button class="btn btn-teal" type="button">Teal</button>
<button class="btn btn-white" type="button">White</button>