Implement CRC16, develop mesh allocation table

- Add crc16 utility function
 - Implement CRC16 for config store, remove old checksum, increment layout version
 - Move UBL mesh store/load to MarlinSettings; increment UBL_VERSION
 - Begin to lay out MAT structure, prototype functions, etc.
 - Rename ubl.state.eeprom_storage_slot to .storage_slot
 - Misc. optimization
 - Cleanup/standardize/improve some messages

This is a work in progress!

Marlin/utility.cpp

@@ -34,6 +34,19 @@ void safe_delay(millis_t ms) {
   thermalManager.manage_heater(); // This keeps us safe if too many small safe_delay() calls are made
 }
 
+#if ENABLED(EEPROM_SETTINGS)
+
+  void crc16(uint16_t *crc, const void * const data, uint16_t cnt) {
+    uint8_t *ptr = (uint8_t*)data;
+    while (cnt-- > 0) {
+      *crc = (uint16_t)(*crc ^ (uint16_t)(((uint16_t)*ptr++) << 8));
+      for (uint8_t x = 0; x < 8; x++)
+        *crc = (uint16_t)((*crc & 0x8000) ? ((uint16_t)(*crc << 1) ^ 0x1021) : (*crc << 1));
+    }
+  }
+
+#endif // EEPROM_SETTINGS
+
 #if ENABLED(ULTRA_LCD)
 
   char conv[8] = { 0 };