Improved thermistor tables

Tests run:

Heated bed
-Determined thermistor was 440K and took beta from here http://www.digikey.com/product-detail/en/175-444QBF-301/480-3154-2-ND/1886040
-Tested heated bed at 22C 50C 75C 100C and verified with IR gun to within 3-4C

Extruder
-Open circuit temperature is 38.5 and adjusted DEFECT to -30
-Displayed -11 on startup
-IR gun was not able to measure extruder temp however:
-At 200 ABS plastic would not extrude
-At 210 ABS could extrude with difficulty and did not come out with smooth texture
-At 220 ABS plastic extruded smoothly

This was on my davinci with no HW modification at all, and no unit specific calibration