Added trade support @ cex.io

This is a first rough shot for EMA trading at cex.io … I've added a NeDB support (local key/value store) to avoid fetching tons of megabytes from cex.io API on each startup.  As cex.io API does only deliver historical data based on trade ID (instead of time), we would need to always fetch tons of data to find the start point for our first OHCL.

This version does already support monitoring/simulation and live trading.