[wallet] Refactor ProcessImport()
[wallet] Refactor ProcessImport()

This commit is move-only and doesn't make any functional changes. It
simply moves code around within ProcessImport() in preparation for
refactors in the next commits.

chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin