Another round of fixes to merged Havoc/Eugene pickling

Several of these are once again picking Eugene's changes
from his branch.

 - move from Seq to Vector in things we will pickle
 - use a Position case class instead of xsbti.Position in protocol
 - define a uriPickler
 - force static only in some focused scopes, but we can't yet
   compile with it everywhere
 - when tests fail to roundtrip log the object we were trying to roundtrip
 - uncomment various commented-out tests that now compile
 - comment out registration of ModuleId serializer since it's broken
   with static only