Improve main layout to be more compliant with Windows 11

[veler]

Is your feature request related to a problem? Please describe.
I got feedback that DevToys isn't fully compliant with Windows 11 layout guideline.

Describe the solution you'd like

Here is an old screenshot of DevToys, by the time called DevTools:

On this screenshot, we were being a little bit more compliant, but the margin of Json Formatter was too big and we were losing too much space.

Here are mock-ups of how we could try to improve it:

Additionally, we could experiment by following what the Clock app does:

• There's a color difference between the navigation view and the page content
• There's no hamburger menu, unless the navigation pane is closed.