[breeze-icons] Add 16px versions of gnumeric-font.svg and link gnumeric-font.svg to font.svg

Summary: This patch adds 16 px SVGs of gnumeric-font.svg and creates a symbolic link for both the 16 px and 24 px versions (font.svg),

Reviewers: VDG, ndavis, GB_2, ngraham

Reviewed By: VDG, ndavis, GB_2, ngraham

Subscribers: GB_2, ngraham, ndavis, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D18794