MapContextEditor: Switch map projection to WGS84

[MrSnyder]

Environment

• Python version: 3.8+
• MrMap version: 1.0-pre

User Story

As a user, I want that the map uses WG84 as map projection, so that all WMS can be used as layer sources (as every WMS has to support WGS84).

Acceptance criteria

• [ ] Given I am a user, when I use the MapContext editor, I want the map to use WGS84 as projection.