Getting code paras excludes the necessary new line at the start

[Bhargav-Rao]

The getCodeParagraphs in PostUtils, is a bit faulty in edge cases.

In markdown, the four spaces creates a code block, only if there is a new line before the starting of the code block.

The getCodeParagraphs function should check this as well.

[sbaltes]

For our SOTorrent project, we developed an extraction method that splits Stack Overflow posts into code and text blocks. Our method considers other Markdown "dialects", for example GitHub's approach using three back-ticks ``` (see also the corresponding test cases). If you'd be interested in integrating that method into Guttenberg, just let me know.