Dictionary sections

Updated version of https://github.com/umbraco/Umbraco-CMS/pull/108.

This isn't really a big thing but adds a bit of hierarchy to reading Dictionary items programmatically.  Now it only prepends parent dictionary names if the dictionaryIsHierarchy setting is set(and uses that value as the glue).  One can still read dictionary sections with that off(assuming the child items start with the parent item's name).

Anyway, no't really a big thing, but I find it useful in our code, so  maybe others can enjoy.  (There is probably a better way to get the same hierarchical logic that this exposes via the node hierarchy, but this was simpler and required less changes to the existing code.