Integrated fixes from henrikbrixandersen pull request #504

Added servo actuated enstop coding to allow G28 command to engage and retract a servo to specified angles.

faster GLCD (ST7920 SW-SPI) implementation / fixes

- fixed long menu entries (>14 or >18 chars) caused overrun in dogm lcd
implementation
- fixed pin set problem when in interrupt
- much faster ST7920 SW-SPI implementation
- increased ST7920 framebuffer size for more speed

Added support for Megatronics v2.0 and Minitronics v1.0

Fix: Long menu entries (>14 or >18 chars) caused overrun in hitachi display implementation

merged from code downloaded from reprapworld.com

Fixed typo in Comment

Revert previous change pin check change

Reviert previous change of #if BLAH_PIN > 0 to #if defined(BLAH_PIN) &&
BLAH_PIN > -1. Unfortunately some times pin 0 is used. For my sins I've
gone through and replaced all unsafe checks of #if BLAH_PIN > -1 with
the safe version.

fixed typo / added "const" to defines for newer gcc compatibility

Add Panelolu2 support for Melzi

fix broken LCD commit #dfa549f2 from buildrob - GLCD/DOGM implementati...

LCD: Added Deadzone at 100% Feedrate

Implement automatic cold-end/extruder motor fan control based on nozzle temperature

Combine and converge other I2C LCD branches (PANELOLU2, VIKI & PCF8575)

This adds a deadzone at 100% Feedrate when changing it at the status
screen/main menu. Prevents from unwanted feedrate-changing when
navigating back to the main menu and makes it easier to return to 100%.

The I2C LCD status indicators now indicate when the hotends or bed are
turned on at all (rather than just when they are in their heating phase)

servosupport

BUGFIXES for temperature.cpp / add RUMBA thermocouple support