Add external list of broken URLs to linkcheck_ignore
merge dev_4_4 -D org -I include -E conflict -E needs-fixes -E broken: PR 379 (Fix source code links moved to the scifio-tools foder)
merge dev_4_4 -D org -I include -E conflict -E needs-fixes -E broken: PR 387 (Metamorph: fix erroneous channel counts)
merge dev_4_4 -D org -I include -E conflict -E needs-fixes -E broken: PR 403 (Add external list of broken URLs to linkcheck_ignore)