Use more appropriate "Alternatives" icon and text

Summary:
The new icon was just added in D20367. The current icon is semantically and visually incorrect,
and the new one fixes that.

The current text also does not begin with an action verb, and this patch fixes that too.

Test Plan:
Before:

After:

Reviewers: VDG, Plasma, GB_2, filipf

Reviewed By: VDG, GB_2, filipf

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D20392