Remove the RMXP map management support

[AerunDev]

As a Game Designer
I would like to be guided to the use of Tiled as a single source of truth
So that my project will be ready for the Version 3.0 migration
And the migration will be easier

Things to know

• For now, a project can still use Tiled mode or RMXP mode
• This mode can be changed in the App settings (Integration > Map management) or by editing the project.studio file
• If a project set the toggle "Use Tiled as a map creation tool" ON, the project is migrated to the Tiled mode and the toggle can't back to the RMXP mode (and this is what we want)
• Any Tiled project should set the Tiled path to make sure they can open and edit their maps with Tiled
• ⚠️ Since 2.8.0, a banner is displayed to any project still using RMXP as a map editor so that they can migrate when they want. This feature will force it.

Acceptance criteria

• Loading a project using RMXP mode will display a dialog to ask the user to migrate to Tiled
• A link to the migration guide is added to the migration dialog
• Make sure that users won't be able to back to RMXP mode by force editing the project.studio file