Improving the guess density for species_full_delta

Description

Improving the guess density for LCAO with species_full_delta. Instead of a uniform guess, the code now use hydrogenic wavefunctions to get the guess. This leads to a much better guess and helps the code to converge.

Test for an all-electron boron atom

LCAO eigenvalues before the change:

Eigenvalues [H]
 #st  Spin   Eigenvalue      Occupation
   1   --   -10.024517       2.000000
   2   --    -2.076272       2.000000
   3   --    -0.246897       0.333333
   4   --    -0.246897       0.333333
   5   --    -0.246897       0.333333

LCAO eigenvalues after the changes:

#  State  Eigenvalue [H]  Occupation    Error
      1       -7.379376    2.000000   ( 1.5E+00)
      2       -0.456895    2.000000   ( 1.2E+00)
      3       -0.234654    0.333333   ( 8.9E-01)
      4       -0.234654    0.333333   ( 8.9E-01)
      5       -0.234654    0.333333   ( 8.9E-01)

Final eigenvalues:

#  State  Eigenvalue [H]  Occupation    Error
      1       -6.334139    2.000000   ( 1.8E-06)
      2       -0.335455    2.000000   ( 1.9E-06)
      3       -0.137147    0.333333   ( 1.1E-07)
      4       -0.137147    0.333333   ( 1.1E-07)
      5       -0.137147    0.333333   ( 1.1E-07)

For this example, the code converges in 16 iterations instead of 24.

News snippet

Improving the guess density for LCAO with species_full_delta.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.