Switching from passing the FOUserAgent for several of the image

Switching from passing the FOUserAgent for several of the image
functions to its internal Avalon logger instead.  (Only object used within
FOUserAgent parameter, plus this library is also used for the PDFTranscoder, plus
FOUserAgent not always available from everywhere anymore.)  Holding off making
a complete switch in this package (FOUserAgent still used in a few more
places, albeit only its logger is being requested)
until others comment.

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@197259 13f79535-47bb-0310-9956-ffa450edef68