Initiate initializr documentation

This commit commit adds restdocs and stub generators and initiate
a reference guide for Initializr.

Most of the controller tests now use MockMvc via a custom version
of the MockMvcClientHttpRequestFactory (from spring-test). The
snippet names are auto-generated in the form

<HttpMethod>/<path>[/queries(/<name-value)*][/headers](/name-value)*]

when there is a comma-separated value in a header it is
abbreviated as <first-value>.MORE.

Wiremock stubs are generated in the same form under
snippets/stubs (with ".json" as the
file extension).

The controller tests that stayed as full stack use a different
base class AbstractFullStackInitializrIntegrationTests.

A long JSON body can be broken out into separate snippets
for each field (or rather a list of fields supplied by the
user). This feature was already used with hard-coded snippets
in the wiki.

See gh-295

initializr-actuator/pom.xml

@@ -65,6 +65,11 @@
 			<artifactId>json-path</artifactId>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.springframework.restdocs</groupId>
+			<artifactId>spring-restdocs-mockmvc</artifactId>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-web</artifactId>

initializr-actuator/src/test/groovy/io/spring/initializr/actuate/stat/MainControllerStatsIntegrationTests.groovy

@@ -17,6 +17,8 @@
 package io.spring.initializr.actuate.stat
 
 import groovy.json.JsonSlurper
+
+import io.spring.initializr.web.AbstractFullStackInitializrIntegrationTests;
 import io.spring.initializr.web.AbstractInitializrControllerIntegrationTests
 import org.junit.Before
 import org.junit.Test
@@ -46,7 +48,7 @@ import static org.junit.Assert.fail
  */
 @Import(StatsMockController)
 @ActiveProfiles(['test-default', 'test-custom-stats'])
-class MainControllerStatsIntegrationTests extends AbstractInitializrControllerIntegrationTests {
+class MainControllerStatsIntegrationTests extends AbstractFullStackInitializrIntegrationTests {
 
 	@Autowired
 	private StatsMockController statsMockController