do not require slf4j 1.7, 1.6 is enough
add non-standard bundle manifest header to make Jetty find taglibs
added org.ops4j.pax.shiro.faces to Require-Bundle

(hoping to help resolve tags)
more tests for shiro-faces in OSGi mode

Pax Web does not recognize Faces tags from imported bundles, so some
test fail (set to @Ignore)