Support logLevel as query parameter to set the navapp log level

It would be nice if the navapp log level could be set by means of a query parameter. This way a developer can see debug logging without having to configure it via the console in the repository.

If this query parameter is present it should override the (server-side) default (configured in the repository of OFF if not). 

Note that it is still useful to set the logLevel globally server side, e.g. to have INFO the default for a test or acceptance environment.