Add Yakuake to terminal emulators

[abhnvkmr]

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• [X] I have carefully read and comply with the Contributing Guidelines of this repo.
• [X] I have searched the PRs of this repo and believe that this is not a duplicate.

- **Title**: Yakuake - **Link**: https://www.kde.org/applications/system/yakuake/ - **Category**: Terminal emulation applications - **Description**: Yakuake is a drop-down terminal emulator which smoothly rolls down from top of the screen upon pressing a hotkey.

[abhnvkmr]

I am closing this PR and endorsing #88 because I somehow missed it going through the list.