Moved the definitions of the LCD_STR_* to Conditionals.h

to avoid errors in Marlin_main.cpp. #1860

In the include tree of Marlin_main.cpp the decision between the display types is not made.
To include the right LCD_STR_* ether 'dogm_lcd_implementation.h' or 'ultralcd_implementation_hitachi_HD44780.h' with all their code.
A 'dogm_lcd_implementation.h.h' would be a curiosity.
So i moved both of the definition blocks to conditionals.h

On the long term it could make sense to use the same numbering for the u8glib and the hitachi symbols.

Marlin/Conditionals.h

@@ -154,6 +154,35 @@
     #endif
   #endif
 
+  #ifdef DOGLCD
+    /* Custom characters defined in font font_6x10_marlin_symbols */
+    // \x00 intentionally skipped to avoid problems in strings
+    #define LCD_STR_REFRESH     "\x01"
+    #define LCD_STR_FOLDER      "\x02"
+    #define LCD_STR_ARROW_RIGHT "\x03"
+    #define LCD_STR_UPLEVEL     "\x04"
+    #define LCD_STR_CLOCK       "\x05"
+    #define LCD_STR_FEEDRATE    "\x06"
+    #define LCD_STR_BEDTEMP     "\x07"
+    #define LCD_STR_THERMOMETER "\x08"
+    #define LCD_STR_DEGREE      "\x09"
+
+    #define LCD_STR_SPECIAL_MAX '\x09'
+    // Maximum here is 0x1f because 0x20 is ' ' (space) and the normal charsets begin.
+    // Better stay below 0x10 because DISPLAY_CHARSET_HD44780_WESTERN begins here.
+  #else
+    /* Custom characters defined in the first 8 characters of the LCD */
+    #define LCD_STR_BEDTEMP     "\x00"  // this will have 'unexpected' results when used in a string!
+    #define LCD_STR_DEGREE      "\x01"
+    #define LCD_STR_THERMOMETER "\x02"
+    #define LCD_STR_UPLEVEL     "\x03"
+    #define LCD_STR_REFRESH     "\x04"
+    #define LCD_STR_FOLDER      "\x05"
+    #define LCD_STR_FEEDRATE    "\x06"
+    #define LCD_STR_CLOCK       "\x07"
+    #define LCD_STR_ARROW_RIGHT ">"  /* from the default character set */
+  #endif
+
   /**
    * Default LCD contrast for dogm-like LCD displays
    */

Marlin/dogm_lcd_implementation.h

@@ -108,22 +108,6 @@
 
 #define START_ROW              0
 
-/* Custom characters defined in font font_6x10_marlin_symbols */
-// \x00 intentionally skipped to avoid problems in strings
-#define LCD_STR_REFRESH     "\x01"
-#define LCD_STR_FOLDER      "\x02"
-#define LCD_STR_ARROW_RIGHT "\x03"
-#define LCD_STR_UPLEVEL     "\x04"
-#define LCD_STR_CLOCK       "\x05"
-#define LCD_STR_FEEDRATE    "\x06"
-#define LCD_STR_BEDTEMP     "\x07"
-#define LCD_STR_THERMOMETER "\x08"
-#define LCD_STR_DEGREE      "\x09"
-
-#define LCD_STR_SPECIAL_MAX '\x09'
-// Maximum here is 0x1f because 0x20 is ' ' (space) and the normal charsets begin.
-// Better stay below 0x10 because DISPLAY_CHARSET_HD44780_WESTERN begins here.
-
 // LCD selection
 #ifdef U8GLIB_ST7920
   //U8GLIB_ST7920_128X64_RRD u8g(0,0,0);

Marlin/ultralcd_implementation_hitachi_HD44780.h

@@ -201,18 +201,6 @@
   #define LCD_STR_PROGRESS  "\x03\x04\x05"
 #endif
 
-/* Custom characters defined in the first 8 characters of the LCD */
-#define LCD_STR_BEDTEMP     "\x00"  // this will have 'unexpected' results when used in a string!
-#define LCD_STR_DEGREE      "\x01"
-#define LCD_STR_THERMOMETER "\x02"
-#define LCD_STR_UPLEVEL     "\x03"
-#define LCD_STR_REFRESH     "\x04"
-#define LCD_STR_FOLDER      "\x05"
-#define LCD_STR_FEEDRATE    "\x06"
-#define LCD_STR_CLOCK       "\x07"
-//#define LCD_STR_ARROW_RIGHT "\x7E"  /* from the default character set. Only available on DISPLAY_CHARSET_HD44780_JAPAN - at this place!*/
-#define LCD_STR_ARROW_RIGHT ">"  /* from the default character set */
-
 static void lcd_set_custom_characters(
   #ifdef LCD_PROGRESS_BAR
     bool progress_bar_set=true