Add support for including custom CSS, JS and metadata tags to a page

[vladbailescu]

As a developer, it would be good if I could easily include CSS link, Javascript script and metadata meta tags in a page. This would be driven by a context-aware configuration and would allow:

• an arbitrary number of such tags to be included
• defining the type of the tag and its attributes
• defining the location of the page where they would be included
• possibility to group all paths under same prefix so that they can be easily updated when using long-term caching

Using context-aware resources, the configuration could look like:

config
     + prefixPath="/some/path"
     - item01
          + element=["link"|"script"|"meta"]
          + location=["header"|"footer"]
          + attributeName="attributeValue"
          ...
      - item02
      ...