Rework icon with higher quality and new color

Change icon color to match the primary color of the theme (i.e.,
`#3a65ab`). The new color looks good on both dark and light surfaces
which solves #155.

Introduce SVG logo instead of PNG for better quality and scalability.

Improve icon creation. Introduce an automated script to create different
logo formats in different sizes enabling easier update of logo from
single place.

build/README.md

@@ -1,5 +1,5 @@
 # build
 
-- These are the file that are used by electron.
-- Logos are created by from the [PNG icon](./../public/icon.png)
-  - by running `npx electron-icon-builder --input=./public/icon.png --output=build --flatten`
+This folder contains files that are used by Electron to serve the desktop version.
+
+Icons are created from the main logo file and should not be changed manually, see [related documentation](./../img/README.md).