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
• [x ] My code file is named according to CONTRIBUTING.md
• [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
• [x ] My code is well commented
• [x ] I have not copied my code from anywhere

[deutranium]

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