Add Parameter Header in V2 API

[luotao1]

In v1 api, there is parameter header in paddle/parameter/Parameter.h

 struct Header {
    int32_t version;     // = 0, file format version
    uint32_t valueSize;  // = sizeof(real)
    uint64_t size;       // = getSize()
  };

While in v2 api, it directly writes f.write(struct.pack("IIQ", 0, 4, size)) in python/paddle/v2/parameters.py#L282：

 def serialize(self, name, f):
        param = self.get(name)
        size = reduce(lambda a, b: a * b, param.shape)
        f.write(struct.pack("IIQ", 0, 4, size))

Thus, we can't use version to distinguish different parameters: such as mkldnn parameters and paddle parameters. So, we should add the parameter header in V2 api too.

related with #3409