remove min width from player stage on test page
background button: fix button sizing and positioning (closes #210)
poster: fix button vertical centering
poster: fix play button size calculation when rendering (closes #212)
add destroy method to plugins to allow for event deinitialization (refs #211)
change container to destroy plugins on its own destroy handler (refs #211)
change core to destroy plugins on its own destroy handler (refs #211)
fix poster mediator event leak (refs #211)
fix background button mediator event leak (refs #211)
background button: change ready call to nextTick to allow for a render cycle to run