Design Rework #5 - New Icons

[LuisMossburger]

Description See also #100 and #118 for progress. This merges the use of two new icon styles derived from four icon packs by Freepik (Flaticon).

• Use colorful, detailed icons for "inside" (list views etc.)
• Use black outline icons for "outside" (text editor, navigation, header)
• Add an imprint fragment to give proper attribution & a navgation item for that in every fragment

Next up: Toasts & Help, Home Fragment, "design sugar".

Affects App design, therefore everyone can take a look. CC @xSabrina @silvia-ivanova-github-rep @claudia3

Notes for Reviewer Please review & comment/approve. Thanks!

[LuisMossburger]

Please rename the commented name. The black sort and library icon is not identifiable as such to me, but we can clarify that in the meeting.

I have written this down for the TOPs of tomorrows meeting!