Add inception/xception model

[lewfish]

At the end of the Planet Kaggle competition, we found that adding Inception to the ensemble improved the score. Unfortunately, the code we were using was problematic because it doesn't assign a unique name to each layer, so we can't use model.load_weights with it. The automatically generated layer names aren't consistent each time you create a new model (the names contain a constant which is global incremented) so they can't be used after the "best" model is loaded from disk after training finishes. We can fix this in a few ways: fix the underlying problem in Keras or report an issue, add unique layer names to the inception code, or use the Xception model builtin in to Keras which appears to be an improved version of Inception and has unique layer names.

[lewfish]

This issue is no longer applicable to the current and future versions of Raster Vision so I am closing it.