Add InitServer function returning the http handler

[ghost]

This is a minimalist approach to somewhat solve #648, #553 and #549. It is minimally invasive and just moves around some code.

I'm looking for feedback on how this could be improved or generally if that's an approach worthy of merging :-)

An example of how this can be integrated into an app lives here: https://github.com/metafex/revel-modules/tree/master/server. Personally I'm running this in production now and don't have any problems with it yet.

The example server module depends on revel/cmd#22 to generate the necessary code in the main function.

[brendensoares]

@metafex I'm very curious to look at this in more detail! I'll try to reply tomorrow after work, but first, sleep. :)

[brendensoares]

👍 great PR