Auto-configure for Thymeleaf conditionalcomments

Add auto-configuration for thymeleaf-extras-conditionalcomments which
allows parsing of conditional comments for IE.

Example:

	<!--[if lt IE 8]>
		<link rel="stylesheet" th:href="@{/styleIE.css}"
		type="text/css"/>
	<![endif]-->

Without this dialect all Thymeleaf attributes are ignored inside the
comment.

Fixes gh-2113
Merge pull request #2113 from BigMichi1/thymleaf-conditional-comments

* thymleaf-conditional-comments:
  Auto-configure for Thymeleaf conditionalcomments