merged from code downloaded from reprapworld.com

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.

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)

- enquecommand with multiple lines "\n" doesn't work -> M140 S0 didn't
get processed. So I wrote a new func for the cooldown which uses
setTargetHotend. In addition this does return to status page after
selection.
    - Added setWatch() to preheat-functions (Temperatur sanity check
would never have worked when preheating from the lcd panel)

The Viki LCD rotary encoder uses a different number of steps per
rotation. This fixes the seeming "missed" steps when selecting a menu.

- changed the variables from keypad to reprapworld_keypad
- added a missing ifdef check

The for loop for Axis count over the Array.
Add a break after M907

Extruder 2 was checked where extruder 1 should be checked.

If S is left out perhaps it should be silent, but check the spec for
this M code.

Also cosmetic comment changes and spelling corrections in printed
messages

(duplicates initialization in Marlin_main.cpp)

Also refactor extruder auto fan logic to simplify further and now only
check every 2.5 seconds

Argument order of lcd_buzz was set to mirror that on tone(). Change
default M300 frequency to something audible.