Fix #510
Fix #510

added:
these options to add-bw-track.pl:
-- clip_marker_color <color>
-- bg_color <color>
-- height <value>

Example:
./bin/add-bw-track.pl --in sampledata/json/volvox/trackList.json --out sample_data/json/volvox/trackList.json --label Wavey --bw_url http://<url>/<jbrowse>/sample_data/raw/volvox/volvox_sine.bw --plot --bg_color "#0f0" --height "150" --clip_marker_color "#f00"

GMOD/jbrowse,erasche/jbrowse,Arabidopsis-Information-Portal/jbrowse,limeng12/jbrowse,GMOD/jbrowse,limeng12/jbrowse,limeng12/jbrowse,Arabidopsis-Information-Portal/jbrowse,limeng12/jbrowse,erasche/jbrowse,Arabidopsis-Information-Portal/jbrowse,erasche/jbrowse,GMOD/jbrowse,erasche/jbrowse,limeng12/jbrowse,Arabidopsis-Information-Portal/jbrowse,erasche/jbrowse,GMOD/jbrowse,Arabidopsis-Information-Portal/jbrowse,limeng12/jbrowse,GMOD/jbrowse,nathandunn/jbrowse,erasche/jbrowse,limeng12/jbrowse,Arabidopsis-Information-Portal/jbrowse,erasche/jbrowse,nathandunn/jbrowse,erasche/jbrowse,limeng12/jbrowse,nathandunn/jbrowse,nathandunn/jbrowse,nathandunn/jbrowse,Arabidopsis-Information-Portal/jbrowse