Move protocol v0/v1 parsing to its own class and request objects

Move protocol v0/v1 parsing to its own class and request objects

Protocol v0/v1 parsing code doesn't have any real dependency on UploadPack.

Move it to its class and use a request object to read the data in
UploadPack.

This makes the code easier to test, keeps similar structure than protocol v2,
reduces the line count of UploadPack and paves the way to remove the
members as implicit parameters in it.

Change-Id: I8188da8bd77e90230a7e37c02d800ea18463694f
Signed-off-by: Ivan Frade <ifrade@google.com>