[cpackget] add support for LicenseSet description added to the PDSC specification

[jkrech]

Describe The Problem To Be Solved
The Open-CMSIS-Pack-Spec has been extended with LicenseSets
This meta information needs to be processed by cpackget.

Suggest a solution
a) All gating licenses need to be extracted after the download and accepted by the user prior to installing the other pack content.
(multiple interactive accepts)
b) If <licenseSets> and <license> are present, <license> is ignored
c) cpackget will not display license by <component> but only those licenses that have the gating attribute set to true
d) if spdx information is provided this is displayed and can be accepted or the full license can be displayed.