Refactor: simplified Parallel_2d interface

[jinzx10]

Reminder

• Have you linked an issue with this pull request?
• Have you added adequate unit tests and/or case tests for your pull request?
• Have you noticed possible changes of behavior below or in the linked issue?
• Have you explained the changes of codes in core modules of ESolver, HSolver, ElecState, Hamilt, Operator or Psi? (ignore if not applicable)

Unit Tests and/or Case Tests for my changes

• The unit test for BLACS functions are redesigned to be more informative.

What's changed?

Parallel_2D, which is the base class of Parallel_Orbitals, has its user interface simplified in order to facilitate the use of 2d block-cyclic distrubtion.

Any changes of core modules? (ignore if not applicable)

No.

[mohanchen]

Great job!!!