B-77840: href filter
add external-href-filter, cleanup XsltFilter, stream xslt on response
delete unnecessary files
add test-utils sub module, add unit tests for external filters
fix mvn build issue, prevent JSON from being XSLT-ed
fix issue when 304 is returned and we got xslt error
refactor, move common code to TransformerUtils
clean up unused imports, add logging, rid of dead code
fix parent relative path
restrict template match @href only to links with certain rel value
Merge pull request #6 from shintasmith/B-77840_href_filter

B-77840: replace the external_href.xsl with a servlet filter