IOS/ES: Keep track of the active title properly

This changes ES to keep track of the active title properly,
just like IOS:

* It is NOT changed on resource manager open/close.
* It is reset on IOS reload.
* It is changed by ES_DIVerify and ES_Launch.

IOS stores the active title in a structure like this:

    struct ESTitleContext
    {
      Ticket* ticket;
      TMD* tmd;
      u32 active;
    };

With this commit, we also do keep the Ticket and TMD around. This
makes some of the DI ioctlvs (which return data about the current
active title) trivial to implement in the future.

This fixes the System Menu not being able to see update partitions
and also allows us to change Dolphin's active game info in the future.

Source/Core/DiscIO/Volume.h

@@ -37,6 +37,7 @@ public:
   }
 
   virtual bool GetTitleID(u64*) const { return false; }
+  virtual IOS::ES::TicketReader GetTicket() const { return {}; }
   virtual IOS::ES::TMDReader GetTMD() const { return {}; }
   virtual u64 PartitionOffsetToRawOffset(u64 offset) const { return offset; }
   virtual std::string GetGameID() const = 0;