HtmlTable interface and implementation

This is an implementation of the Table interface in https://github.com/darcy-framework/darcy-ui/pull/25 .

It is for simple html `<table>` tags structured semantically. Tables implemented with more complicated dom and/or with richer capabilities (such as a http://www.datatables.net/) can have their own implementations.

To describe a particular HTML table's domain, you can write your own column definitions via HtmlColumn<T>. Some basic implementations can be included like String based columns or Link columns, etc.