Introduce a properties-based PippoSettings object

Pippo and it's modules really need some flexibility in configuration and this, IMO, must be provided by pippo-core.

This PR introduces a properties-based PippoSettings object and instruments the appropriate points in pippo-core to make it accessible to Application, Initializers, etc.  This is a simplified variation of the code that powers Gitblit's settings and is an alternative to adding a dependency on something like Commons-Configuration which adds 400-600KB to the core footprint.