Drop go.rice support

[markbates]

While the go.rice project has been helpful in being able to create fully packaged binary, it has also caused more problems than I want, namely the panic around not being able to find ../public/assets. That one happens a lot!

The package also prevents Buffalo apps from run on GAE #213, while it not the only package preventing us to get on GAE, it is definitely one of the bigger ones.

In v0.8.0 I will be remove support for go.rice in both the buffalo build command, as well as inside the resolvers package. It will be replaced with another package I have been working, but have to release. More details as they come.

Branch can be found here: https://github.com/gobuffalo/buffalo/tree/packr
Repo here: https://github.com/gobuffalo/packr