This is the last cut that was in #1117 before i closed that PR
This PR allows a user to set the flag "ta_on_candle" in their config.json
This will change the behaviour of the the bot to only process indicators
when there is a new candle to be processed for that pair.
The test is made up of "last dataframe row date + pair" is different to
last_seen OR ta_on_candle is not True