Anchor wasn't properly used in ApiFlowBasePost

There's a bit of code that will check values for
$value instanceof Anchor. Since Anchor was not used,
it couldn't match those to Flow\Anchor, and would not
execute that code.
As a result, Anchor objects weren't ->toArray()'ed,
and returned badly formed API results.

Also fixed namespace order in *Get
Also removed unused UUID namespace in *Post

Change-Id: Iff2251b91857bf3434560a35109d802cd70e81e5