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/ubl.h

@@ -30,8 +30,9 @@
   #include "planner.h"
   #include "math.h"
   #include "vector_3.h"
+  #include "configuration_store.h"
 
-  #define UBL_VERSION "1.00"
+  #define UBL_VERSION "1.01"
   #define UBL_OK false
   #define UBL_ERR true
 
@@ -92,7 +93,7 @@
   typedef struct {
     bool active = false;
     float z_offset = 0.0;
-    int8_t eeprom_storage_slot = -1;
+    int8_t storage_slot = -1;
   } ubl_state;
 
   class unified_bed_leveling {
@@ -117,10 +118,6 @@
       void display_map(const int);
       void reset();
       void invalidate();
-      void store_state();
-      void load_state();
-      void store_mesh(const int16_t);
-      void load_mesh(const int16_t);
       bool sanity_check();
 
       static ubl_state state;
@@ -153,9 +150,6 @@
 
       static bool g26_debug_flag, has_control_of_lcd_panel;
 
-      static int16_t eeprom_start;    // Please do no change this to 8 bits in size
-                                      // It needs to hold values bigger than this.
-
       static volatile int encoder_diff; // Volatile because it's changed at interrupt time.
 
       unified_bed_leveling();
@@ -351,7 +345,5 @@
 
   extern unified_bed_leveling ubl;
 
-  #define UBL_LAST_EEPROM_INDEX E2END
-
 #endif // AUTO_BED_LEVELING_UBL
 #endif // UNIFIED_BED_LEVELING_H