fixed nonce, open order api call and added in ema signal type

fixed nonce issues with more than 1 api call per second, its ugly but works.
fixed api call for open orders, need to find a more graceful way of handing success or fail from the api
added in ema signal type based on http://sentdex.com/sentiment-analysisbig-data-and-python-tutorials-algorithmic-trading/calculate-exponential-moving-average-python/