Download version-appropriate ADMX files

[Fleex255]

The Windows 11 policy definitions are neither a superset nor subset of the most up-to-date Windows 10 policy definitions (source). This means there are some policies that are only listed in the Windows 11 ADMX files and some others that are only in the Windows 10 ones.

This is a problem for the Help | Acquire ADMX Files feature in Policy Plus because it should guarantee that at least all applicable policy definitions are acquired. (It's also potentially undesirable to obtain inapplicable policy definitions, as mentioned in #52.) Policy Plus should be improved with:

• A way to select the desired set of policy definitions to download
• Automatic detection of the appropriate set based on host Windows version
• Possibly a way to unify the Windows 10 and 11 definitions (maybe outside the Policy Plus program itself)