Update language_de.h with MSG_MOVE_E1 - E4

MSG_MOVE_E1 was missing
MSG_MOVE_E2 was missing
MSG_MOVE_E3 was missing
MSG_MOVE_E4 was missing

I assigned "0" to "MSG_MOVE_E1", "1" to "MSG_MOVE_E2" and so on, as this is what i assume to be the standard naming for the first (E0) and second (E1) extruder. This would have to be changed inthe other languages too :(