Fix crash on SUSE when setting temperature due to setting temp field background color to "".

This replaces "" strings that cause aborts in python-wxWidgets wxColour_helper with
Python None objects. This corrects an abort where the helper tries to fetch the
first byte of the colour string even when it's 0 length.

Update webinterface.py

oops! :'( web/css/style.css

attempting fix for issue 305

need to explore CherryPy & websockets, but this quick'n'dirty is a big
speed increase

Encountered https://github.com/kliment/Printrun/issues/305#issuecomment-12306186
This edit removed the error, but I don't know what the original output was so I'm not sure if this really _fixes_ it, or is just a band-aid.

experimental branch: fixing broken pyreadline download url

fixing broken pyreadline download url

[printcore] Have print_thread rejoin execution thread.

[printcore] Switched to use Python if syntax and not Ruby's.

Add checking to pause/resume functions in printcore.py

Confirmation on exit

Make sure to set target temps to 0 before exiting.

To ensure safety, we make sure we set target temps to 0 before we exit
pronsole.

Presently, one might accidentally terminate a print with a CTR-D while
printing. Now we ask the user to confirm exiting if there is a print
going when they try to exit.

Protect the user from typos in setting the extruder temp by confirming
them with the user if they exceed 250.

Conflicts:
	gcoder.py

Support M82/M83 for relative E

Show connection error to the user

Clean up echoed firmware lines, connect info.

Presently, when you connect to a printer using pronsole, one sees
something like:

uninitialized>start
uninitialized>Printer is now online
uninitialized>echo: External Reset
printer>Marlin 1.0.0 RC2
...

With a few carriage returns and some string hackery, we clean up
the output so that one sees:

No port specified - connecting to /dev/ttyACM0 at 115200bps
start
Printer is now online
External Reset
Marlin 1.0.0 RC2

Much cleaner!

Clean up the monitor command.

The monitor command now:

* Has more pythonic code
* Limits precision of progress elements (12.3% instead of 12.347812...%)
* Uses a carriage return to have print progress replace the previous
  progress line.

For example:

Monitoring printer, use ^C to interrupt.
Updating values every 5.000000 seconds.
Print progress: 0.3%

Previously, the line "Print progress: 0.3%" was "Print progress: 0.2%",
etc.

Fancy configurable prompts!

* Prompts are now generated based off of string templates,
  for example: "%(bold)sT:%(extruder_temp_fancy)s %(progress_fancy)s
  >%(normal)s "

* We have a dictionary of prompt string templates for different
  situations.

* We have bold support for the prompt.

* We have extruder temperature support for the prompt.

* We have progress support for the prompt.

Before, when there was an error while connecting, user didn't know, when
Pronterface wasn't launched from the terminal.

So you could just hit Connect button several times and all you've get was:
Connecting...
Connecting...
Connecting...

Now, when there is an exception during the connection, the user will notice:
Connecting...
Error: You are trying to connect to a non-exisiting port.

Or:
Connecting...
Error: You don't have permission to open /dev/ttyUSB0.
You might need to add yourself to the dialout group.

Unfortunately pyserial's SerialException doesn't provide errno yet, so the
message isn't so user friendly:
Connecting...
could not open port None: [Errno 2] No such file or directory: 'None'

I've filled a bug report with patch to pyserial.

Together with this I've realised, there is unnecessary UTF8 decoding of the
output. When user has UTF-8 locale, there was an exception when printing the
exception to the output (almost an exception inception). So I have dropped it,
but feel free to add it back, if I broke anything else.