Document the included samples in the docs again so there's some continuity from v1 docs, while making it clear they're not best practice examples but instead illustrate solutions to various use-cases.
* Added new corda and cordaRuntime configurations for cordapps to be able to explicitly depend on Corda and exclude corda dependencies from the fatjar
* Added corda integration section to docsite to describe how to integrate with Corda.
* Updated more of the documentation to reflect the new method of specifying core corda dependencies.
* Reorganised document logic to move all build system related documentation to the cordapp build systems page.
* Renamed cordapp build systems doc to match actual purpose.
* Improved the warning for building against a net.corda dependency in a cordapp
* Added a line of dialogue to show further reading for those reading about writing cordapps.
