Configure logging for tests.

org.apache.xmlgraphics asks for a configured log4j-logger.
To harmonize output, the AOP-based logging was also changed
to log4j.
Manage aspectjrt version.

The aspectjrt version is now managed in the parent pom.

Signed-off-by: KayErikMuench <KayErikMuench@users.noreply.github.com>
Parser and iterator are maven modules

Managing reqifparser and reqifiterator as maven modules
simplifies building.

Signed-off-by: KayErikMuench <KayErikMuench@users.noreply.github.com>
Implementing a listener iterator.

Clients of this iterator can register implementations of
the listener interfaces for ReqIF-Types defined in the
ReqIF data structure.
Whenever the iterator detects a ReqIF-Type for which a
listener is registered, this listener is called with the
related object of that type.

Signed-off-by: KayErikMuench <KayErikMuench@users.noreply.github.com>