LCD: Added Deadzone at 100% Feedrate

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%.
Merged from Upstream Master
soft tab correction
fixed merge
Merge pull request #486 from xifle/Marlin_v1

LCD: Added Deadzone at 100% Feedrate