[Feat] Handle Non-Group expenses.

[sub1120]

Background

This issue is continuation for #66, where we handled only Group expenses.

What need to be done?

Write functionality to handle Non-Group expeses. Here "Non-Group expense" is term used to denote such expenses which are directly created amount friends #79.

Detailed Explaination

Implementor can add details according to their understanding. We also keep updating issues as we progress.