Fixes #209: Handling argument list containing 0s in NumberPartition

[lumapools]

Description

• Instantiating NumberPartition with a list that contains at least one 0, i.e. [0, 3, 7, 9] will show a warning: Warning: Omitting zeros in the numbers list. Instantiate with keep0=True to keep 0 terms.
  and remove the 0s from the list, unless the user specifically states to keep the zeros by instantiating NumberPartition with the keep0=True argument (False by default).
• If keep0=True but the list does not contain any 0s, then the list remains unchanged.
• If keep0=True and the list contains at least one 0, then no warning is displayed and the list remains unchanged.
• Fixes Warning if 0 is passed in numbers_list in NumberPartition problem #209

Checklist

• I have performed a self-review of my code.
• I have commented my code and used numpy-style docstrings
• I have made corresponding updates to the documentation.
• My changes generate no new warnings
• I have added/updated tests to make sure bugfix/feature works.
• New and existing unit tests pass locally with my changes.

Type of change

• New feature (non-breaking change which adds functionality) [optimization]

How Has This Been Tested?

• Tested locally by manually instantiating different cases of NumberPartition and changing the list arguments and keep0 to see the functionality outside unit tests.
• Written unit tests for different cases that cover the code additions

Name the new unit-tests that you have added along with this change.
In test_problems.py, added a unit test test_number_partitioning_handles_0_in_numbers()