Add option to download images via wget instead of rsync

Should be callable via `bash sync_images -q`
Download OMERO images using wget rather than rsync on Travis build
Remove images under omero/developers and fix image links
merge dev_4_4 -D org -I include -E exclude: PR 368 (Cpp: Correct content and markup)
merge dev_4_4 -D org -I include -E exclude: PR 407 (Move OMERO images out of the Git repository)