[1.5.x][ENTESB-5152] fix jbpm-workitems-camel-qs: add slf4j package import

[psiroky]

• also change the code a bit to make sure the accepted/rejected file always exists, otherwise the FileReader fails on non-existing file

@cunningt could you please review and merge?

[psiroky]

Merged into 1.5.x as https://github.com/jboss-integration/fuse-bxms-integ/commit/0c67d896fa334178b75cfa56ba68a0ac75277fea