Support aggregated reports at each level in the multi-module hierarchy

The current system makes the assumption that if one wants aggregated reports one does not want further javadoc reports (aggregated ones) down the hierarchy. We do require this functionality and in fact do the same for all our reports (PMD, Checkstyle, Clover, JXR, Surefire, etc):

A->B->C->D1 (JAR)
A->B->C->D2 (JAR)
A->B->E(JAR)
A->F (JAR)

A - javadoc for D1,D2,E,F
B - javadoc for D1,D2,E
C - javadoc for D1,D2
D1 - javadoc for D1
D2 - javadoc for D2
E - javadoc for E
F - javadoc for F

This way there is the required info at the appropriate level throughout the hierarchy. And nope we dont care about space or generation times