[keycloak-dev] Hacking on Keycloak docs

I've updated the main README.md in the GitHub repo to include some details on how to build and run Keycloak. As we had some developer related docs in GitHub wiki (https://github.com/keycloak/keycloak/wiki) and some in repo itself (https://github.com/keycloak/keycloak/tree/master/misc) I've deleted the out of date stuff and moved everything to https://github.com/keycloak/keycloak/tree/master/misc. I've also added a Hacking on Keycloak guide (https://github.com/keycloak/keycloak/blob/master/misc/HackingOnKeycloak.md).