New logo & About dialog
Created by: IlyaBizyaev
This commit replaces all vector and raster copies of the logo with the new one. The new logo is considered simpler, more suitable for small icons, and also fixes transparency.
The About dialog change was required to fix bigger logo display. It replaces an OverlaySheet, which was used in a way conflicting with Kirigami HIG. As a bonus, it is able to change layout direction depending on screen size.