[Performance] Cache stock prices when retrieving

[eleow]

For the front-end, instead of always retrieving the last closed stock prices for all the tickers, we should cache them for better performance. So that only the first request per day needs to be done!

Since there are many possibilities of stocks and start and end date, we need to also consider a unique identifier for our cache file, maybe using MD5

[eleow]

Generate MD5 hash based on input params (timezone, end date, number of datapoints to consider and tickers), so that we can cache results