Overflow menu / Dropdown component: no closing on included buttons

[mfranzke]

In case of buttons (and not links) being used within our overflow menu or dropdown components, we're both not providing and programmatic possibility to close them, as well as not even closing these components ourselves e.g. on a recognized click event within. The latter might be easier / nicer regarding developer convenience, but we should make a quick research how other frameworks are handling this and adapt accordingly.