Improve Row descriptions

[groue]

This PR improves the formatting of Row's description and debugDescription in order to help debugging.

(lldb) po ["name": "foo", "name": "bar", "score": nil] as Row
[name:"foo" name:"bar" score:NULL]

The changes are most visible in adapted rows, and especially rows that contain scopes:

(lldb) po try Row.fetchOne(db, "SELECT 0 AS a, 1 AS b, 2 AS c", adapter: ScopeAdapter(["suffix": SuffixRowAdapter(fromIndex: 1)]))!
▿ [a:0 b:1 c:2]
  unadapted: [a:0 b:1 c:2]
  - suffix: [b:1 c:2]

This PR is intended to bring support for Associations, which will rely heavily on adapted rows, and will sometimes need this debugging tool.