Allow passing a title to Gnuplot.
Allow passing a title to Gnuplot.

This is done via the `title' query string parameter.
This isn't exposed in the UI yet.

Change-Id: I919eaba79f2e22bc6306dc33f87230335da6a644

OpenTSDB/opentsdb,sidhhu/opentsdb,ShefronYudy/opentsdb,andyflury/opentsdb,johann8384/opentsdb,johann8384/opentsdb,eswdd/opentsdb,OpenTSDB/opentsdb,eswdd/opentsdb,andyflury/opentsdb,OpenTSDB/opentsdb,MadDogTechnology/opentsdb,MadDogTechnology/opentsdb,alienth/opentsdb,sidhhu/opentsdb,kidaa/opentsdb,alienth/opentsdb,kidaa/opentsdb,ShefronYudy/opentsdb,MadDogTechnology/opentsdb