User Upgrade Permissions 2.1.0

• Requires php 7.0+
• Requires XenForo 2.1+
• Now depends on Standard Library by Xon
• Confirmed XF2.2 support

This add-on appears to have no compatibility issues with XF2.1

• Ensure a purchased upgrade is applied after receiving payment (aka ignore the canPurchase check run when applying an upgrade).
  • The canPurchase was unexpectedly running under the guest user which produced incorrect outcomes when applying 'usable by user groups'.
  • It is strongly recommended that a manual audit of monthly user upgrades is done to verify the upgrade was applied, and if not apply a manual upgrade with the expected start/end date.