Fixes for logger resource configuration in dev mode

Fixes #1741.

There are two fixes for the issue included.

A logger resource won't be found in dev mode when the reloadable application provider does an early initialisation of logging because the application classloader is not yet created. The `Logger.init` method now only uses the default logback configuration and doesn't attempt the full configuration using application resources and configuration.

If the configured logger resource is not found the fallback file used is now located in the application `conf` directory.