stepping stone GmbH will be a reseller like everyone else
Use PROJECT_SOURCE_DIR instead of CMAKE_CURRENT_SOURCE_DIR to be compliant with the rest of the code.
Add a copy of icon.png as about_image.png to separate the two images.
Add cmake module with macro to generate Qt resource files (taken from ParaView).
Regenerate main_window ui file with a recent version of Designer to get rid of the build-time warnings.
Rename reseller image to about image and separate it

Sepiola (the vanilla client) currently uses the same image as Window
icon and as image in the about dialog, while branded versions of Sepiola
usually have two distinct images. Assuming that Sepiola itself has two
distinct images (even though they are in fact the same at the moment)
simplifies the build logic.
Make the bug-report link a clickable link
Cleanup reseller/branded build system
Generate brandable logos/images Qt resource file at cmake time

The window icon and the about image are brandable. We are following
ParaView on this (effectively using a macro from them) and generate the
Qt resource file to incorporate the window icon and the about image at
cmake ("configure") time instead of including them in the main resource
file "screen.qrc".