[NixFifty] Gift Upgrades 2.4.3

Fix anonymous gifts not being marked as anonymous as expected.
Fix "Cannot call method canGiftTo on a non-object (NULL)".
Fix incorrect visibity on the _postDelete() method in the GiftUpgrade entity.
Fix a potential issue where gifted upgrades were not marked as such.
Add additional indexes to xf_user_upgrade_expired/xf_user_upgrade_active tables.

• Only inject User Essentials templates if that add-on is active.

• Allow recurring upgrades to be gifted. The first term will be paid for by the gifter and the giftee can choose to renew upon its expiration.
• Expose Recent Gift Post's widget date limit as a configurable option.
• Add missing relation to the UserUpgradeExpired entity.
• Fix potential issues surrounding the giving of free gifts.