Improve SLF4J Bindings for tests and runtime of SOLR
SOLRJ relies on SLF4J, no binding are listed. SOLR-webapp (used in test) relies twice on SLF4J with JUL binding. One can be removed (the maven import) the other can't (the war loaded by jetty and present in src/main/resources).
Jena relies on SLF4J.
Since we rely on JCL+LOG4J we define a LOG4J as default SLF binding.
But this is still not fully satisify since some error message are printed both in test and at runtime in a webapp. This should be investigated to find the right configuration of these various and conflicting logging frameworks.