toString() now prints out incoming message data
Removed redundant toString() implementation
Added hexToByteArray(String) method
BitFields, enemies and friends same packet type

The "action" and "args" mechanism has been replaced by a BitFields
class, with bits represented by enums.

Thom changed enemy and civilian vessels to be handled by the same code,
and the protocol reflects this now; the same packet type delivers
information on both. This commit updates the code to handle this now,
but more work is still needed. (Don't know how to determine friend from
foe, for example.)

The old, unused SystemInfoPacket class has been removed.