added binary atan2 op
added atan2 img op
added atan2 to img calculator dialog
Merge pull request #54 from knime-ip/imgcalculator-atan2

Thanks @DanielSeebacher
ScifioImgSource: Fix bug in close of underlying image source

closeNow() called close() of the wrapped reader, which in turn called
close(false) on the wrapper itself, which did nothing. calling close(false)
directly solves this problem.
Merge branch 'master' of https://github.com/knime-ip/knip