Task #49162: Rewrite install tool
Folder not writeable should be an "Error" not a "Warning"
The Install Tool checks for permissions in it's folder structure. Currently if files cannot be written to a directory this is considered a Warning. Thus it is not displayed with a "red badge" in the main menu of the Install Tool.
But not being able to write to typo3temp, uploads or fileadmin might cause several other places to fail. Thus we should rise this status message to "Error" instead.