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-expression/spring-expression.gradle

@@ -0,0 +1,6 @@
+description = "Spring Expression Language (SpEL)"
+
+dependencies {
+	compile(project(":spring-jcl"))
+	compile(project(":spring-core"))
+}