Strongly Connected Components algorithm added into Graph category (C++)

[jvillegasd]

Submission Checklist

• [* ] Your pull request targets the master branch of the repository.
• [* ] You have only one commit (if not, squash them into one commit).
• [* ] You have read the Contributing guidelines and your changes follow them.

Type of Change

• [ ] Bug fix
• [* ] New implementation

PR Description

Implementation of Strongly Connected Component on DAG using C++.

Issue #[Add issue number here.]