Preferences design changes

[jamesreprise]

What is the goal of this PR?

We've made adjustments to the behaviour of the preferences dialog after some internal feedback. End users should notice a more pleasant UI/UX. Contributors and developers should notice little difference other than working examples of a multiline text input within a form to base future development off of.

What are the changes implemented in this PR?

Ticked items have been completed.

• [x] Spacing of Cancel/Apply/OK buttons.
• [x] Spacing for preference group content.
• [x] Menu bar entry for preferences.
• [x] Checkbox alignment.
• [x] Multiline text area for ignored paths.
• [x] Selected page not highlighted on dialog launch.
• [x] Spacing of navigator entries.

[grabl]

PR Review Checklist

Do not edit the content of this comment. The PR reviewer should simply update this comment by ticking each review item below, as they get completed.

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Code

• [x] Packages, classes, and methods have a single domain of responsibility.
• [x] Packages, classes, and methods are grouped into cohesive and consistent domain model.
• [x] The code is canonical and the minimum required to achieve the goal.
• [x] Modules, libraries, and APIs are easy to use, robust (foolproof and not errorprone), and tested.
• [x] Logic and naming has clear narrative that communicates the accurate intent and responsibility of each module (e.g. method, class, etc.).
• [x] The code is algorithmically efficient and scalable for the whole application.

Architecture

• [x] Any required refactoring is completed, and the architecture does not introduce technical debt incidentally.
• [x] Any required build and release automations are updated and/or implemented.
• [x] Any new components follows a consistent style with respect to the pre-existing codebase.
• [x] The architecture intuitively reflects the application domain, and is easy to understand.
• [x] The architecture has a well-defined hierarchy of encapsulated components.
• [x] The architecture is extensible and scalable.

[alexjpwalker]

It would be nice if we could line up the first line of the text field with the label on the left.

Currently it feels like the text in the text field is too low. Moreover, when we type subsequent lines, it feels like the spacing between lines is correct, so it's just the first line that is misaligned.