DonationNag: ask after each major update (#10213)

This changes how the donation nag timing works.

The donation nag will now appear:

- after a major update (e.g. 48 -> 49)*
- once in late july
- once in december

however, a donation nag will never pop up more than once a month. So, if there is an update on the 26th of November, and you get a popup on the 28th, you will not get one in december.

This is of course still disableable in your config.

src/managers/DonationNagManager.hpp

@@ -10,7 +10,16 @@ class CDonationNagManager {
     bool fired();
 
   private:
-    bool m_bFired = false;
+    struct SStateData {
+        uint64_t epoch = 0;
+        uint64_t major = 0;
+    };
+
+    SStateData getState();
+    void       writeState(const SStateData& s);
+    void       fire();
+
+    bool       m_bFired = false;
 };
 
 inline UP<CDonationNagManager> g_pDonationNagManager;