Console displaying errors and prints in a <pre> tag

[AngelaRemolina]

This PR resolves #8
A console is shown on the bottom part of the iframe. Here is displayed the result of the print() function and errors.
Here is a gif of how it looks and works:

Note: This is one approach where the console.error, console.debug, console.info and console.log function is redefined to log in screen as well. A better aproach is under construction #12

[AngelaRemolina]

The last commit adds the highlight.js module so errors get highlighted with colors.
The position of the <pre> element is on top when is an error and on bottom when is a print() statement.

[AngelaRemolina]

This approach works but we have chosen to use this one #13