Added e2_steps_per_unit
Added e2_steps_per_unit to ConfigurationStore.cpp
fixed typo
added e2_steps_per_unit declarations
changed num EXTRUDERS to 2
renamed e2_steps_per_unit to e1_steps_per_unit
lowered current for dual-extruder motors
versioned up the EEPROM_VERSION and adjusted data order
added logic in planner.cpp to use correct e_steps for the active extruder
added lcd menu item for e1_steps_per_unit
set best guess extruder offsets for dual-extruder
merge dual_extruder_calib into master