Refactor UI files

[LateusBetelgeuse]

In order to ease the maintenance of the UI, reduce the amount of code, improve its performance, provide a common API for all files, improve the UX in general, and be more prepared for Qt 6, all QML files need some (maybe huge) refactoring. This includes, but is not limited to:

• Get rid of all global variables.
• Get rid of most algorithms and logic programmed in Javascript.
• Get rid of unneeded ScrollView instances and other expensive items.
• Improve delegates since they are the most expensive objects.
• Get rid of duplicated Dialog objects.
• No component should access a property that is meant to be private in another component.

This is the visual part of #351.
#363 will be, eventually, a blocker for this issue.