Implement usage of .well-known URIs

### Description

[RFC-5785](https://tools.ietf.org/html/rfc5785#section-3) defines a path prefix for "well-known locations", i.e., `/.well-known/`. [Paulheim and Hertling](http://iswc2013.semanticweb.org/sites/default/files/iswc_poster_17.pdf) suggest the usage of `/.well-known/void` to gather VoID information regarding the datasets available in the server. The parser should implement this behavior.

A previous implementation of #118 would increase the impact of this feature.

### Solution

* The Frontier could offer the addition of classes which are allowed to "extend" the list of new URIs based on internal rules. For the case described above such a class would simply go through all new URIs, extract the domains (maybe together with their path information as discussed in the paper) and add `/.well-known/void`. Since we can assume it to be a dereferencable URI, the type of this newly generated URI can be set as well.

Start by reading the parser and Frontier implementation, focusing on how newly discovered URIs are collected and extended. Define how domains and optional path information produce `/.well-known/void`, then verify that the generated URI is treated as dereferenceable and assigned an appropriate type.

Written by the indexing model from the issue text.