Draw custom indicators on chart

[bludnic]

Proposed solution:

export function* customStrategy() {
  // ...
}

customStrategy.indicators = {
  RSI: (candles, options) => calcRSI(candles, options),
  MA: (candles, options) => calcMA(candles, options)
}

The indicators property is intended for the client only. We need a way to send the indicator functions from the backend to the client so it can be used for drawing indicators on charts.