Moved section on DC + git to guides from reference.
Merge pull request #406 from KevWright/design-center-update

Moved section on DC + git to overviews from reference.
Modified DC overview with copied content
Merge pull request #407 from KevWright/design-center-update

Modified DC overview with copied content
Added DC content to the glossary.
Merge pull request #408 from KevWright/design-center-update

Added DC content to the glossary.
Added more content to some DC docs
Merge pull request #409 from KevWright/design-center-update

Added more content to some DC docs