Update build.fsx using Paket

[sergey-tihon]

Most of build scripts in our projects contain the same targets and differ only in constant values generated during init.fsx phase

If we move all project specific configs to separate files like project.yaml we should be able to reuse build.fsx in projects without modifications.

This should allow up update build.fsx in all project without painful merge effort.

Does it make sense for you? @forki @pblasucci

[pblasucci]

I'm generally in favor of this idea (though I do tend to modify my build.fsx rather heavily...)