Add TB HTML Token replacement with basic includes library

# Summary
Added the Talent Brew Token replacement functionality in to the generator utilizing the "grunt-string-replace" plugin. This processes "index.html" and replaces any "<!--** **-->" comments with the contents of an HTML file in the dev/includes directory whose file name matches the string contained within the TB-style comment. I did not include this into the build tasks since we will want the tokens in their original form for the production code. Also enabled the task to execute with live-reload.

# To-do
- Manage the "includes" directory as a Bower dependency - have it pull the folder from a git repo.
- Alternatively have the back-end team expose the token names and their matching contents as a JSON object accessible through a web API (when hell freezes over).