GUI v2: Footer

[apyrgio]

Main issue: #885

Add a footer to our Dangerzone app, which will show the Dangerzone version and some quick actions. These actions are:

• View tutorial: ❗ to be added once we have a tutorial in our https://dangerzone.rocks site
• Settings: The default settings that apply to all files.
• Burger menu: The burger menu that Dangerzone has, with the following extra entries:
  • About Dangerzone: ❗ placeholder, we don't have content for it yet
  • Report an issue
  • View previous conversions: ❗ placeholder, we don't have an issue for that yet

Most likely this will be the issue that will introduce the new buttons. These buttons have:

• rounded corners
• an outline
• embedded icons
• a shadow hint

Design material

Footer for welcome page

Footer for default settings

Footer for the rest of the app

Expanded burger menu