Consolidated .registerPreLoadedApps() into .registerApps().

Based on @markhealey's comment in https://github.com/OpenF2/F2/pull/68#issuecomment-18155702 I consolidated .registerPreLoadedApps() logic into .registerApps() so there is only one entry point. This also increased complexity by allowing a mix of both pre-loaded and traditional F2 requested apps.

With this change I added documentation comments to the code, you will need to run <code>node build -y</code> to see the changes as I did not commit the doc changes, to call out the different use cases. In addition to the code/comments I updated the unit tests to reflect the changes. All unit tests were verified locally and with Travis-CI.

Let me know if you have any issues/suggestions.