Remove QtGui-Dependency

[GeraldKimmersdorfer]

The dependency of QtGui inside the nucleus makes our WASM file significantly bigger

Issue includes:

• Search for usage of QtGui inside nucleus (hopefully mostly QImage)
• Replace the functionality with smaller libraries
• Make sure that all changes are appropriate

Goal:

• Faster Emscripten linking time and smaller WASM file size for web compilation

[GeraldKimmersdorfer]

done with 9fd8cdc5950e7ca79d1230f94371dd4a2e99e6a2

Made a quick comparison showing that WASM size is reduced by more than 50% and build times are reduced by around 20s on my cpu:

first value is full build, second value are consecutive builds

=== WASM ===

== no qt::gui ==
release: 1:05 | 0:38 (5MB)
debug:   0:49 | 0:22 (41MB)

== with qt::gui ==
release: 1:39 | 1:14 (12MB)
debug:   1:04 | 0:40 (60MB)

=== NATIVE (Vulkan) ===

== no qt::gui ==
release full: 0:33 | 0:06 (9MB)
debug full:   0:30 | 0:05 (40MB)

== with qt::gui ==
release: 0:34 | 0:10 (9MB)
debug:   0:32 | 0:10 (40MB)