fix mercurial diffs, should change to cloned repo first

Dependencies

• [2] ODWGRX32 check for revisions
• [3] SHYRGAWZ hydra: when no external url is given for diff's of git/hg input, revert to a diff done on a local available clone
• [4] TH674WKJ add log diff to compare logs to previous builds
• [5] HZ2U4QEV no branch info available yet in scmdiff, so disable for now
• [*] BKOIYITR added some json responses

Change contents

• replacement in src/lib/Hydra/Controller/API.pm at line 220
  [3.552]→[2.130:189](∅→∅)
  − $branch = `hg log --template '{branch}' -r $rev2`;
  [3.552]

  [2.189]
  + $branch = `(cd $clonePath ; hg log --template '{branch}' -r $rev2)`;