Added Data.Collections.BulkInsertable + instances.
Changed Eq/Ord instances for SuccessorNodes.

Only the URL and the node state are taken into account now. The the
problem with comparing the result is that it's (a) expensive (in the
case of large binary data) and (b) often not possible (in the case of
SomeExceptions in Failures).
Fixed Map-instance for Data.Map
Finished Fetch.Forest.