Created Issue: Add option for package dependency without reference ("soft" or "implicit" dependency) [3077]

There have been more and more cases in my recent experience where I use a package that has "soft" dependencies on other packages. These "soft" dependencies are necessary for the package's libraries to function, but are not needed by the actual project using the package.

I know you can set explicit references for a package that limit what is referenced from the lib folder of the package. However, it would be very handy to have similar functionality for package dependencies and controlling the need for referencing them. An example follows.

* Package A depends on Package B, but the project/solution need not have a reference to the assemblies in Package B.
* When Package A is included, Package B is also downloaded **and referenced**.
* Now the user of the project may have needless classes and Intellisense pollution.

Certainly, if the user explicitly chooses to use Package B, a reference should then be added. There are also plenty of cases where the author of Package A intends for Package B to actually be referenced. However, there are times where the author would like to indicate that the dependency on Package B is "soft" or "implicit" and not necessary as a reference in the target project.

This would essentially make Package B's assemblies bin deployable.