Move check for empty hand to Hand class
Remove word_is_valid

SinglePlayer and MultiPlayer word checks will need to be very different.
The simple abstraction of word_is_valid would not have been sufficient
(WIP) Add word lookups for multiplayer games

Also reordered some packet numbers, typedef'd the map for keeping track
of word positions in grid (useful for multiplayer).
Remove TODOs, add comments, fix message priority
Missing break statements in switches
More debug messages for packet code
Handle dumping in multiplayer
Add TODOs