[NuGet] Check NuGet packages when project target framework changed.

Show warnings about packages needing to be reinstalled in the Package
Console.

Add Reinstall menu option for a package in the Solution pad so a NuGet
package can be uninstalled and installed with one action.
[NuGet] Add tests for package compatibility checks.

Ensure project target framework changed events do not fire for all
project properties that are changed.

Ensure packages needing reinstallation are highlighted in Solution pad
with warning text and icon.

Ensure incompatible packages are detected, marked in the
packages.config file, and shown in the Package Console.