Update fields.lua

Fix:
  As it was, fields.lua was generating  a runtime error when trying to build/parse incoming 4B chunks.

Suggested changes:
- in outgoing 0x4D, renaming "Manipulation Type" to just "Type" to be consistent with incoming 0x4B's "Type"

- In incoming 0x4B: some of the comments are out of sequence.
- in incoming 0x4B, _unknown5 is listed twice. Renamed to 6 and renumbered all the following unknowns.
- in incoming 0x4B's function:  only processing the "FULL" 88-byte packet when Type matches the hardcoded  Set does not seem like the right thing to do, as there are other Type numbers with an 88-type packet. Plus there might be more. Changed function to process it differently depending on length of data instead. 
- in incoming 0x4B, renamed "Sender Name" to "Player Name" as the field is used for both for senders and recipients (depending on whether this is for inbox or outbox)

Other issues:
- Some of the existing comments with observed values are not accurate (or no longer accurate)
- 'Packet number' field does not seem to be a packet number.  unknown4 seems to be for a packet number for when they come in pairs.

There's more to do, but I wanted to push this as is for now.
Update fields.lua
Update fields.lua

moved original comments around
Update fields.lua

reverted size check, and went back to checking for types in set (added 0x04)
Merge pull request #1095 from mujihina/patch-3

Update fields.lua