Fix case in a couple of includes (Marlin.h, Configuration.h).

This fixes Ultimaker2Marlin build on case-sensitive file systems like one usually has on Linux.

W/o the fix:
```
  CXX   /usr/share/arduino//hardware/arduino/cores/arduino/Tone.cpp
  CXX   UltiLCD2.cpp
UltiLCD2.cpp:1:27: fatal error: configuration.h: No such file or directory
 #include "configuration.h"
                           ^
compilation terminated.
make: *** [applet/UltiLCD2.o] Error 1
```
With the fix:
```
  CXX   applet/Marlin.elf
  COPY  applet/Marlin.hex


AVR Memory Usage
----------------
Device: atmega2560

Program:  110004 bytes (42.0% Full)
(.text + .data + .bootloader)

Data:       5474 bytes (66.8% Full)
(.data + .bss + .noinit)


   text    data     bss     dec     hex filename
 109466     538    4936  114940   1c0fc applet/Marlin.elf
```

I tried to preserve ```\r\n``` ends of lines, but it's better to verify.