Implement Google Programmable Search Engine (PSE) on doxygen content heading

[loricooperhdf]

As discussed in our documentation meeting... Replace the doxygen search in the top nav bar with the google PSE.

<script async src="https://cse.google.com/cse.js?cx=f671574fa55cc44e6">
</script>
<div class="gcse-search"></div>

We do have a variety of customization options to change the look and feel.