Added some spacing and a border to the blocks.

[AaronSadlerUK]

I have added a 4px top margin plus a border to make the blocks distinguishable with each other.

I was unable to the css stylesheet to load so it's also inline, not sure if that's a limitation of the backoffice?

Fixes #5

[rickbutterfield]

I'm a little torn on this one - in my opinion the preview should appear as close to the live site as possible but I get the need to be able to see the separation of blocks without having to hover/tab through them.

[robertjf]

@AaronSadlerUK @rickbutterfield an alternative to this is to add some markup to the Component Views to inject a class based on the IsBlockPreview extension method - that way you can style the padding/margin/border any way you like without having to inject CSS etc.