More elaborated tracker-search source

Working towards multiline candidates 'helm-source-tracker-transformer can
handle (DISPLAY . REAL) cells and builds them now.

To make that possible, a new attribute 'source-candidate-seperator (not
yet documented) is queried in 'helm-output-filter--process-source. It
defines the 'split-string SEPERATOR by which the raw output source is
split. This is needed to make the raw candidates arrive in one piece in
form of
"  file:///path/to/foo
  ...foo snippet..."
Another approach for the tracker-transformer

This transformer function works without changes in the process-filter by
saving incoming incomplete candidates temporarily in a variable.
Merge remote-tracking branch 'refs/remotes/upstream/master' into mod-only-tracker
Add github reference for 'multiline issue
Remove test-candidate from tracker-transformer
Improved tracker-transformer

Reduced complexity of the transformer function.
Disabled color for tracker-search output.
Highlight paths with 'helm-highlight-files.
Added github reference.
Merge remote-tracking branch 'upstream/master' into mod-only-tracker

Conflicts:
	helm-files.el
Merge remote-tracking branch 'refs/remotes/upstream/master' into mod-only-tracker
Moved to cl-loop, removed helm.el modifications
Merge pull request #533 from scrathat/mod-only-tracker

tracker-transformer with paths/snippets selectable and generic keymap