misc FIXES in realtime

cc @agramfort @LauriParkkonen @Eric89GXL @mluessi 

I am not able to build the docs on my computer. I remember there was some problem when using `plt.ion()` but I added a `plt.show()` at the end which should hopefully what sphinx finds. Any suggestions?

also, the `decim` parameter doesn't seem to work in `RtEpochs`. The data does not seem to match the offline data. If I add `decim=2` to http://goo.gl/GQ2OHZ and `decim=2` to http://goo.gl/tmYlmG, the test hangs. Not yet sure what's wrong ...