Code formatting in Markdown

[dri94]

Currently, when creating an Xblock we have some basic markdown support such as using square brackets for creating a checkable list. However, we do not seem to have full markdown support. When creating an Xblock using the code formatter ticks '`', tries to create an algebraic formula rather than work as a code formmater.

We should fully support markdown in the Xblocks to enable staff to create a wide range of problems.