Ability to show a calibration grid (150mmx150mm) and modify the scale, size and offset to calibrate the projected image.

Tested on both wx2.9 and wx2.8, shouldn't bring any regression.

Should remove the need for workarounds such as
http://t00tiereprap.wordpress.com/2013/04/02/messy-custom-button-placement-in-pronterface/

This change is based on an IRC discussion with @Triffid_Hunder, @Sound and
reifsnyder, where we figured out that the best way to report multiple extruders
temperature would simply to add more information to the M105 line in the form of
T0:a/b T1:a/b... The "T:" part should still report the active extruder tool by
default, or obey the T gcode parameter).
This change also simplifies the parsing by using a generic regexp.

This is mainly done by using the file-like interface of socket objects.