[keycloak-dev] Support for installed applications added (including example)

Support for installed applications in form of two special redirect uris (urn:ietf:wg:oauth:2.0:oob and http://localhost) has been added. There's also a basic example. To try it out start the server as normal, create an app for it (mark it as public). Download the keycloak.json file. Then run: # mvn -pl examples/demo-template/customer-app-cli install exec:java -Dexec.args="<path to keycloak.json>" You can then run different commands to try it out. It has two different ways to login the user: * login-desktop: this opens a ServerSocket on a local port, opens the login url in the browser, after login the ServerSocket is used to retrieve the code * login-manual: this uses the 'urn:ietf:wg:oauth:2.0:oob' redirect to display the code in the browser and the user has to manually copy/paste this into the application