Provide .get(), .set() helpers, refactor config

[robertrossmann]

This provides the .get() and .set() functions on app.config object.

.get()

The function takes a string, which will be treated as an object path to a property on the config object. If that property exists, it will be returned, otherwise it will default to undefined.

.set()

The function takes a string, which will be treated as an object path to a property on the config object and a value, which will be set on the given property path. If any properties in the path do not exist, they will be created.

I refactored the whole config stuff into its own class to provide better encapsulation.

Closes #124

[robertrossmann]

Please do not merge, alternative approach might be chosen. Discussion continues in #124. I'll leave this open for the time being.

[tjwebb]

@Alaneor closing until we settle on a solution. Thanks.