Add support for hot reloading of configuration files

There are two scenarios where hot-reloading of Ninja configuration files
would be very useful:

1. reloading localized messages files while in dev mode (i.e. realtime externalization)
2. reloading externally specified application configuration for all runtime modes
Allow application.conf to be reloaded in dev mode
Make hot-reloading of external config optional (default: off)
Merge pull request #235 from gitblit/hotreloads

Add support for hot reloading of configuration files