Chord improvements

[jordi]

1. Copy the package planet.chord into packages planet.chord.sigcomm and planet.chord.improved.
2. Apply the following improvements into the planet.chord.improved Chord version:

• Build dynamic Finger Tables (with dynamic size, according to the DIFFERENT known neighbors).
• Allow a cache of known nodes (may be including the finger table itself), by looking up NodeHandles? in any RouteMessage?.
• Update the Finger Table with NodeHandle appeared in RouteMessage? during its normal routing.
• Build ChordId? for enabling ids from 2 to 32 bits (implementing on the current ChordId? class or another).