Added key binding from Lua possible

- Possible to add key bindings from Lua possible. This calls Lua scripts
  from key commands.

 - Temporary fixed a small bug for volume rendering

scripts/bind_keys.lua

@@ -0,0 +1,21 @@
+
+openspace.clearKeys()
+
+function setEarthAsOrigin()
+	openspace.setOrigin('Earth')
+end
+
+interaction_speed = 2.75
+
+-- Key Bindings
+openspace.bindKey("f1", "setEarthAsOrigin()")
+openspace.bindKey("f2", "openspace.setOrigin('Mercury')")
+openspace.bindKey("f3", "openspace.setPropertyValue('Earth.renderable.enabled', true)")
+openspace.bindKey("f4", "openspace.setPropertyValue('Earth.renderable.enabled', false)")
+openspace.bindKey("f5", "loadKeyBindings()")
+
+
+openspace.bindKey("U", "openspace.distance(-interaction_speed * openspace.dt(), 13.0)")
+openspace.bindKey("J", "openspace.distance(interaction_speed * openspace.dt(), 13.0)")
+
+openspace.bindKey("PRINT_SCREEN", "openspace.takeScreenshot()")