Refactor code

So far, the code has grown organically. We should refactor the code to reduce duplication and improve maintainability.

Useful links

• https://refactoring.guru

added T: task label

mentioned in commit 8a7c30b6

mentioned in commit 7dbed4af

mentioned in commit 8d707131

changed milestone to %GTK Next

mentioned in merge request !89 (merged)

I decided to go with the MVC (Model-View-Controller) pattern to achieve "more" Single Responsibility for MainWindowContainer in !89 (merged). In general I think I'll split all containers into controllers and views.

In the same !89 (merged) I also converted most containers to views to have consistent names throughout the code. However, some views have no controllers which should be fixed in future refactoring work.

assigned to @nicoalt

mentioned in merge request !93 (merged)

changed milestone to %GTK 0.1.0-beta3

closed with merge request !93 (merged)