Fixed layout should be dynamic

[glaslos]

The App.svelte has a lot of hard-coded layout glory. This makes is rather difficult to add new layout elements without breaking the current layout. Even adding new pages would be challenging. Here are some offenders:

Redo the layout allowing for:

• Dynamically resize the window
• Adding more elements (like separating the right column)
• Adding a new page (e.g. rule management, user profile...)