This commit changes the way the Tee in Pronterface works. When no log is
specified, sys.stdout is redirected as before to a tee between the
console panel and the true sys.stdout. When a log is specified,
sys.stdout is untouched and logging output is saved in both the console
panel and the log file.
The side effect is that all output must now go through the logging
module to properly get in the console panel and in the log.
Now we have to catch all "print" statements =)

Also cleanup a minor detail in stl plater

This reverts commit a2c0d7a4.

We used to have our own gcode analyzer in gviz but this was clearly
suboptimal and broken. Position of drawn things should not differ in
anyway from the original GCode anyway.

Use precmd() method instead of adding our own layer of preprocessing

FIX: Unable to connect on Debian testing

Lasercutting: Relative moves with the jog dial should move with G0 instead of G1

This simple workaround should simply ignore initial layers with little
to no movements, and thus avoid M190/M109 to destroy ETA prediction.