Drop the aopalliance:aopalliance dependency

As of Spring 4.3 RC1 the `org.aopalliance` interfaces are once again bundled
with `spring-aop` [1]. Moreover, all modules with a dependency on
`aopalliance:aopalliance` directly or indirectly also depend on `spring-aop`.

This change drops the `aopalliance:aopalliance` dependency in all places it's
declared. Where applicable an explicit dependency on `spring-aop` was added in
its place. (This dependency was already present in most places; in one case the
module didn't require `aopalliance:aopalliance` in the first place.)

The documentation is updated accordingly.

[1] https://jira.spring.io/browse/SPR-13984

itest/context/spring-security-itest-context.gradle

@@ -2,7 +2,6 @@ apply plugin: 'io.spring.convention.spring-test'
 
 dependencies {
 	compile project(':spring-security-core')
-	compile 'aopalliance:aopalliance'
 	compile 'org.python:jython'
 	compile 'org.springframework:spring-aop'
 	compile 'org.springframework:spring-beans'