JsonConfig: FormattedField regex accepts format fields like "{myfield:02}"
Added TiledVolume class and a basic test.
Added OpTiledVolumeReader
OpInputDataReader: Added tiled volumes as a supported format
RequestPool: Reverted to the "simple" implementation that doesn't clean completed requests until all requests are finished.  This is hopefully a workaround for issue #989 (and #934).  Our RAM usage will be worse, but at least we should be stable again.