kcms/effects: Add context to i18n string

Similar to how it's written in KWin Scripts KCM.

other minor changes:

Relax minor version import restriction on Kirigami module

We still keep major version number around though, because it used to cause issues with path resolution without it.

Fix license headers

Project description isn't present anymore in other files.

Add myself to copyright header

Seems fair, since I refactored those UI files recently.