Refactor: eliminate most use of LOWF instance in esolver - step 1

[kirk0830]

What's changed?

In this PR I do the following things:

1. add free function(s) to do the readin of LOWF file. Because it is the I/O of psi, I place them in module_psi
2. add comments recording the refactor plan in codes, especially in esolver
3. replace the use of lowf->paraV with orb_con.paraV (waiting to be removed furtherly in the plan of removal of ORB_control)
4. change the way to write code, say from

a = b = c = d;

to

a = d;
b = d;
c = d;

The code before change is hard for maintain and meaningless to performance.

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)

Linked Issue

Fix #4272

Unit Tests and/or Case Tests for my changes

• A unit test is added for each new feature or bug fix.

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

• Example: I have added a new virtual function in the esolver base class in order to ...

[mohanchen]

Good job!