Finalizing improve startup time for fresh or rollback'd session

Finally fixed the long-sought InputStream reading bug from
TransferableGraphFileReader.InputChannel.read(ByteBuffer).

The ByteFileReader implementation expected the provided
ReadableByteChannel to always provide a full buffer of data unless EOF
was encountered and the InputChannel.read implementation was not taking
care of that.

Also added simpler utilities for reading TG's from files/InputStreams
directly using static TransferableGraphFileReader.read(File/InputStream)
methods.

PlatformUtil.readTG can now finally use TransferableGraphFileReader for
maximal performance.

refs #7835

Change-Id: I170986bf271a409f9205fad808ae029becc1d3a4