Clean and extract Parameter functionalities.

[reyoung]

As we need to develop paddle::Parameters concept in C++ (which described in PR #2249), the paddle::Parameter will be heavily used. But paddle::Parameter is heavy and mixes many functionalities in ONE Class. It is necessary to clean paddle::Parameter first. The following jobs should be done.

In PR #2271, the several things are fixed.

• Extract paddle::getTlsTempBufs to parameter::getThreadLocalBuffer.
• Clean unused functions
• Remove Parameter::getPrefetchMatrix function. getPrefetchMatrix is quite simple, should not be extracted as a member function.

The following jobs are under developing.

• Extract ParameterUpdaterHook into ParameterUpdater.
• Extract save/load/random functionalities to a global function or object.

[reyoung]

Closed because we would do a fundamental refactoring for Paddle