* Rebasing changes against master.
* Added back withTx().
* Fix using new error type.
* Moving back database initialization back into the struct.
* Fix failing migration tests.
* Fix linting errors.
* Renamed database object names to be consistent.
* Fixing linting error in imports.
* Rebasing changes against master.
* Added back withTx().
* Fix using new error type.
* Moving back database initialization back into the struct.
* Fix failing migration tests.
* Fix linting errors.
* Renamed database object names to be consistent.
* Fixing linting error in imports.
* Adding missing change from merge.
* Fix error name.
Deprecate the pieceinfo database, and start storing piece info as a header to
piece files. Institute a "storage format version" concept allowing us to handle
pieces stored under multiple different types of storage. Add a piece_expirations
table which will still be used to track expiration times, so we can query it, but
which should be much smaller than the pieceinfo database would be for the
same number of pieces. (Only pieces with expiration times need to be stored in piece_expirations, and we don't need to store large byte blobs like the serialized
order limit, etc.) Use specialized names for accessing any functionality related
only to dealing with V0 pieces (e.g., `store.V0PieceInfo()`). Move SpaceUsed-
type functionality under the purview of the piece store. Add some generic
interfaces for traversing all blobs or all pieces. Add lots of tests.
