EZAudioPlotGLKViewController add _bgcolor member data, record bgcolor. _bgcolor used for hand glkView:drawInRect else condition
remove bgcolor data member.

add glClear(GL_COLOR_BUFFER_BIT) method at begin of glkView:drawInRect
remove two call of glClear in glkView:drawInRect:
Merge pull request #5 from wdwen/master

EZAudioPlotGLKViewController add _bgcolor member data, record bgcolor. _...