Move modules to independent build files

The main `build.gradle` file contains now only the common build
infrastructure; all module-specific build configurations have
been moved to their own build file.

Issue: SPR-15885

spring-context-indexer/spring-context-indexer.gradle

@@ -0,0 +1,8 @@
+description = "Spring Context Indexer"
+
+dependencies {
+	testCompile(project(":spring-context"))
+	testCompile("javax.inject:javax.inject:1")
+	testCompile("javax.annotation:javax.annotation-api:1.3")
+	testCompile("org.eclipse.persistence:javax.persistence:2.1.1")
+}