Set the `maven.compiler.source` property to 1.6

Since forgerock-parent 1.2.6, we need to specify that property in addition to `maven.compiler.target`.

IntelliJ can now import the project properly (using Java 6 style instead of Java 5 for code).

git-svn-id: https://svn.forgerock.org/openig/trunk@685 dbb9e58e-28e6-4ce0-90e8-f11d9605b710
CR-5165 OPENIG-364: Update doc on capturing exchange

git-svn-id: https://svn.forgerock.org/openig/trunk@686 dbb9e58e-28e6-4ce0-90e8-f11d9605b710