Added depth first search in kotlin

[InLieuOfLuna]

This PR implements the code for Depth First Search in Kotlin referred in issue #139
I have read the contributing guidelines in CONTRIBUTING.md and have ensured the following:

• [x ] My code is placed in the required directory as outlined in CONTRIBUTING.md
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• [x ] Variables, classes, functions etc. follow camel case as outlined in CONTRIBUTING.md
• [x ] My code hasn't been implemented or claimed by someone else and I have checked the present issues and PRs for the same
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[deutranium]

Wow, this code is really good and well-commented!

Thank you for contributing!

[deutranium]

On a side note, you can select the checkboxes by typing [x] instead of [x ]
Happy coding!