Add Switcher by @tkgka

[tkgka]

1. [X] Project URL:https://github.com/tkgka/Switcher
2. [X] Update contents.json instead of README
3. [X] One project per pull request
4. [X] Screenshot included
5. [X] Avoid iOS or open-source in description as it is assumed
6. [X] Use this commit title format if applicable: Add app-name by @github-username
7. [X] Use approved format for your entry