Add support for development dependencies

[davidfowl]

In the project.json file, let the developer specify that a dependency is development time only depednency:

{
  "dependencies" : {
    "StyleCop" :  { "version" : "1.0-alpha-*", "type": "development" }
  }
}

This means it'll only be a dependency for meta programming and other development time activities.

parent #37

[Alxandr]

Isn't it cleaner to have it under a different key? Like "devDependencies" or something?

[davidfowl]

Nope, we want to have different kinds of depednencies, dev is just one of them.

[borgdylan]

Could we also have compile time dependencies so that the language service stuff does not get added to the project compilation?

[borgdylan]

Also could there be dependencies that you compile against, but then not get added to the nuspec? (example: packages with contracts for which runtimes have facades already)

[davidfowl]

Yep, take a look at #37

[davidfowl]

Closing this as this doesn't actually describe what needs to be done. We've added basic dependency types now we need to implement some of them.