Better dialog error when trying to create a project with an already existing name and the projects limit hit error.

[ValentinBuira]

This PR improve the dialog error given to user when trying to create a project and sync project. Instead of giving a dump of the server error we display only the part that matter to the users

So far we handle

• Project with an already existing name
• projects limit hit error
• Storage limit error
• Another syncing process running

This PR also relies on another PR in the mergin python api client (see : MerginMaps/python-api-client/pull/209 )

resolve #599 resolve #561

Before:

After: