[cpackget] Add dedicated command to list all installed pack versions with known new version

[jkrech]

Describe The Problem To Be Solved
As a user I want to be able to get a list of installed packs that have a more recent version published so that I am aware of updates to consider for my projects.

(Optional): Suggest A Solution
Add a new command to cpackget that checks the installed pack versions and compares the latest installed pack versions against the latest available pack versions (in .Web\index.pidx and .Local\*.pdsc).

  cpackget list updates

(I suggest to align the command line of cbuild and csolution more using sub-commands rather than flags)

I would leave it to the user to have run the command cpackget update-index for fetching the index and pdsc files of the latest available pack versions.