have AccountDB use address hash for uniqueness (#1533)

* partially done alternate migration scheme

* finish altering migration framework

* migrate tests to new migration framework

* address comments

* remove superfluous newline
[ci skip]

* TempIdx -> TempIndex
[ci skip]

* modify account_db to work on address hash, not address

* add a database migration for new accountdb

* preserve first 96 bits of keys when combining

* handle metadata keys in migration and preserve first 96 bits

* fix comments and hash address instead of hash

* different migrations based on pruning

* migrations mutably borrow self

* batch abstraction for migration

* added missing licence headers

* overlay recent v7 migration

* better error handling, migrate version key as well

* fix migration tests

* commit final batch and migrate journaled insertions

* two passes on journal to migrate all possible deleted keys