Add help-donate-[currency] icons

Summary:
These are only 16px icons.
According to the bug report, these will be used in the application menu, which shows 16px icons.
22px versions can be added later.
FEATURE: 407372
FIXED-IN: 5.59

Test Plan:

Reviewers: VDG, sitter, broulik, ngraham

Reviewed By: VDG, sitter, ngraham

Subscribers: ngraham, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D21526