Clean up special serial port cases

Assume SERIAL_PORT 0 if not defined. Collapse un-numbered register
special case. Clarify comments.

Use the right pins for Gen7 1.4

Marlin v1 configurable serial port

This change makes the choice of serial port configurable so that
wireless capability can be easily added by connecting Bluetooth modules
(such as BlueSmirf or JY-MCU) to the expansion port pins.

Change required after pulling from ErikZalm.

Took out the ifdef when I split 1.4 out and forgot to permanently
define it for <=1.3.

Fix num of digits on LCD for E and Z axis.

Fixed wrong code (will not even compile when EXTRUDERS>2)

This reverts commit cb02c2f9d8.

The number of steps per mm often contains 4 digits before the decimal point and does not require precision greater than 0.1

fix LCD temp bed artifacts on power up ' B022/0.) -> B022/000 '

Create an explicit rule for building applet/Marlin.cpp.

Italian language support

It would seem that the pattern matches do not work when the source
file is created when make is running. The result of this is that it is
necessary to run "make" twice to build the firmware.

This adds an explicit rule without a pattern match for building
applet/Marlin.cpp it corrects the make behaviour at the cost of adding
a little redundancy in the Makefile.

Added Russian translation

Marlin v1

Remove unwanted artifacts in merge of bed-pid tree

PID for heated bed

fix max endstop pins

Spanish language updated