ccd_defs.json: SONY ILCE-5100

Added support for Sony Alpha 5100 (ILCE 5100).

Source for sensor length:
http://www.dpreview.com/products/sony/slrs/sony_a5100/specifications

ccd_defs.json

@@ -300,6 +300,7 @@
   "SONY DSC-W7": 7.176,
   "SONY DSC-W80": 5.75,
   "SONY ILCE-7S": 35.8,
+  "SONY ILCE-5100": 23.5,
   "SONY NEX-5T": 23.4,
   "SONY NEX-5R": 23.4,
   "SONY NEX-7": 23.5,