Add support for stable ordering and dump of views.

[groue]

This pull request fixes two runtime errors regarding database views (CREATE VIEW AS ...).

Requests created with withStableOrder() no longer throw when used on views:

// NEW: views with stable order
let request = Table("myView").all().withStableOrder()

Dumping the content of views with dumpTables() no longer throws:

// NEW: dump tables or views
try dbQueue.dumpTables(["myTable", "myView"])

By default, the rows of views are printed in the order specified by the view, which may be undefined. Pass stableOrder: true in order to guarantee a stable order, suitable for testing:

try db.execute("""
  CREATE VIEW playerName1
  AS SELECT name FROM player;

  CREATE VIEW playerName2
  AS SELECT name FROM player ORDER BY name;
  """)

// playerName1 rows are printed in an unspecified order.
// playerName2 rows are printed sorted by name.
try dbQueue.dumpTables(["playerName1", "playerName2"])

// playerName1 rows are printed in a stable order.
// playerName2 rows are printed in a stable order.
try dbQueue.dumpTables(["playerName1", "playerName2"], stableOrder: true)