Expose an asset router

[cescoffier]

The router will ease the computation of "src" and "link" in templates

[cescoffier]

This feature is already provided by the +routes+ object.

[cescoffier]

My fault, no it's not completely true.

[cescoffier]

Fixed.

Two features were implemented:

1. /assets provide a list of all available assets including the assets included in webjars.
2. an asset method was added to the route object injected in thymeleaf template. So you can write:

<link th:href="${#routes.asset('css/bootstrap.min.css')}" rel="stylesheet"/>
<link th:href="${#routes.asset('css/bootstrap-theme.min.css')}" rel="stylesheet"/>
<script th:src="${#routes.asset('jquery.js')}"></script>
<script th:src="${#routes.asset('js/bootstrap.min.js')}"></script>

It computes the final URL.