Fix incomplete permission list

Hello,

The F-Droid website currently shows an incomplete permission list when an app requires certain permissions such as PACKAGE_USAGE_STATS or ENFORCE_UPDATE_OWNERSHIP (example – see #403 (closed)), and shows an empty permission list when an app requires no permissions (example). Yesterday I submitted the merge request !1120 (closed) that proposes to solve the latter by completely removing the permission list for apps that require no permissions.

This merge request is an alternative based on the work by @redplanet in !446 (closed) that shows missing permissions in the former case and shows "No permissions" in the latter case. Compared to !1120 (closed), merging this would not only fix empty permission lists but it would also fix incomplete permission lists (issue #403 (closed)).

Results:

• package missing the PACKAGE_USAGE_STATS permission: before merge / after merge (the permission is no longer missing)
• package missing the ENFORCE_UPDATE_OWNERSHIP permission: before merge / after merge (the permission is no longer missing)
• package not missing any permission: before merge / after merge (no change)
• package requiring no permissions: before merge / after merge (the message "No permissions" is shown)

Supersedes and closes !446 (closed)

Closes !1120 (closed)

Fixes #403 (closed)