Implement SAVE / LOAD query

[kmaehashi]

This PR implements SAVE / LOAD query to JubaQL system.

The syntax is as follows:

SAVE MODEL model_name USING path WITH ID = id
LOAD MODEL model_name USING path WITH ID = id

For example, in development mode,

SAVE MODEL test USING "file:///home/data/models" WITH ID = test001
LOAD MODEL test USING "file:///home/data/models" WITH ID = test001

will save a model file to / load a model file from /home/data/models/test001/0.jubatus.
You need to use hdfs:/// instead of file:/// for production mode.

Notes:

• This patch updates the required Jubatus client library version to 0.8.0 to use new save RPC that returns a path to the model file.
• This patch depends on (WIP) Improve saveModel / loadModel jubatus-on-yarn#8.
• Documentation needs to be added once this patch got merged.