outline CreateJoiningParticipant function
LoadWallet and SaveWallet changed

Now, LoadWallet and SaveWallet also check against and update the
wallettree. This isolates other functions and packages from needing to
be aware of the wallettree.
Update scriptapi

Move scriptapi.go to package delta.
Scriptapi calls no longer return a cost, only an error.
Scriptapi calls can directly modify a wallets balance.