fix 2 bugs found during testing.
Prevent partial serial data from blocking the SD reading.
Lower the required temperature increase for the heating error. There is more variance in the UM2 heaters then measured before.
Moved reading of MAX6675 from ISR to updateTemperaturesFromRawValues()

Initialized SD card Chip select in tp_init.
Merge https://github.com/marwijn/Ultimaker2Marlin
Minor correction for the display of the nozzle temperatures during cooling down for multi-extruder environments
Merge pull request #51 from Mike-3/master

Minor correction for the display of the nozzle temperatures
Merge pull request #50 from marwijn/master

Changes to allow the use of MAX6675, without causing problems on the SD card.
Allow for compiling without a heated bed.
Fix material menu when no bed is enabled.
Add detailed info for advanced maintenance menu.
Fix the positioning of the error messages
Merge branch 'master' of github.com:Ultimaker/SecretMarlin
Slightly adjust how the bed leveling points are handled.
One more fix for the no bed option. And improve the material load/unload procedure.
Small config change for improve the material load/unload procedure.
Also use the easier load code on first run.
Configure the bowdentube length in the config file.
Do not show bed temperature in the material settings detail view.
Slight compile fix.