Put dependency diagnostics in the lock file

[davidfowl]

Today the DNX has a rich set of diagnostics that are computed from the lock file on compile and inside of design time host (and it should also do that after restore is complete but it doesn't today). These diagnostics are super useful and are used for things like:

• Unresolved dependencies
• Mismatched dependencies
• Incompatible dependencies

If we stored all of the diagnostics in the lock file, they could be shown by any tool that consumed the lock file. We also introduced a bunch of error codes so that tools like visual studio could link to help pages about the topic.

[emgarten]

Moving to 4.3 to track adding warnings/errors to the assets file.

[davidfowl]

When is 4.3?

[emgarten]

2017 Update 1

[rrelyea]

I'm unsure if "update 1" is a thing.

I've updated "4.3" milestone to describe it as:
4.3 will be the working name of the next major update after 4.1.
POR: It will ship with what is internally called VS 2017 "15.3"