JENA-583: Make log4j and slf4j-log4j12 <optional>
JENA-583: Make log4j and slf4j-log4j12 <optional>

This closes #117.

apache/jena,apache/jena,apache/jena,CesarPantoja/jena,CesarPantoja/jena,apache/jena,apache/jena,apache/jena,apache/jena,CesarPantoja/jena,CesarPantoja/jena,CesarPantoja/jena,CesarPantoja/jena,CesarPantoja/jena,apache/jena