Add "In" and "Out" before code

Related to issue #289.

Fix problem when PR #252 was merged.
Fix extra line in IPython output template
CSS arrow to mark input and output

**Note**: This is a prototype.

Instead of "In" and "Out" use arrow to mark the input and output
of IPython lessons.

To construct the arrows we only use CSS.
Remove extra space in sql lessons
Merge pull request #325 from r-gaia-cs/css-arrow

Some fix for IPython Notebook's Template