RTC revamp (#1867)

* get this started

* implement DSi RTC commands

* set up RTC clock timer. lay down basic idea of a clock.

* make the date/time registers writable

* move RTC state to its own structure, to make it easier to deal with

* more RTC work
lay base for date/time dialog

* get the bulk of the RTC functionality going

* much simpler design for RTC stuff

* aha, that is what it is

* start working on the RTC IRQ

* implement all types of RTC IRQ

* start refining sleep mode. code still kinda sucks.

* implement keypad IRQ

* refine it some more

* shut the fuck uuuuuupppppppppppppp

src/Platform.h

@@ -337,6 +337,9 @@ void WriteGBASave(const u8* savedata, u32 savelen, u32 writeoffset, u32 writelen
 /// @param writelen The number of bytes that were written to firmware.
 void WriteFirmware(const SPI_Firmware::Firmware& firmware, u32 writeoffset, u32 writelen);
 
+// called when the RTC date/time is changed and the frontend might need to take it into account
+void WriteDateTime(int year, int month, int day, int hour, int minute, int second);
+
 
 // local multiplayer comm interface
 // packet type: DS-style TX header (12 bytes) + original 802.11 frame