Adds fallback to culture defined on node

[dvandevliet]

This update fixes a null exception when the scope has no language set.

Explanantion For invariant content the language property is always null for the variant. The call to SetCulture will throw a null exception when passed a null value. In that case we need to set the language on the scope by retrieving the culture information for that node and use that to set the language.

[dvandevliet]

I was too quick with this pull request. The current code only works for a node that has culture set on itself. Running into issues with calling ancestors. So changed the status to draft for now.

[dvandevliet]

Updated the pull request. It now thandles these cases:

• retrieve language from culture defined on current node or ancestor
• when all nodes set to inherit culture, it has fallback to the default language

[dvandevliet]

I moved the fix into the controller since there was already some culture resolving taking place. The case where culture is retrieved from domains is now used also for GetMarkupForBlock.

[rickbutterfield]

Fixes #18 and #20