Fix change track color and add experiment color
Fix change track color and add experiment color

The track by default checks for existing attributes then sets the
missing the attributes in the config.

* Add single experiment track color [COGE-305]
* Fix track color cookie support

	modified:   jbrowse/plugins/CoGe/js/View/Track/Wiggle/MultiXYPlot.js

LyonsLab/CoGe_plugin,LyonsLab/CoGe_plugin