Reading wikipedia

This commit contains basic tools to load Wikipedia graph to Cassovary:

1. RedirectsExtractor - tool to parse Wikipedia dumps and get all redirects to a single file.
2. DumpToGraphConverter - tool to parse Wikipedia dumps and print links graph as adjacency list for Cassovary
3. HashMapsBasedWikipediaGraph - classes that read Wikipedia graph and redirects from previous tools and store them in a graph and hash table.

Using this code it's possible to load Wikipedia to Cassovary. Steps take following times (on server class machine):
1. Redirects - 2000s
2. Dumps to Graph - 1800s
3. Reading - 304 s.
They are almost same as those from utils (in our context at least) and you don't need to specify ExecutionContext explicitly, so I don't think we really need to use `external` library for this.