buy_max_amt was working only on live, now it works also on paper mode

Get rid of that annoying message. Telegram tested and working fine.

Previously the training was starting too early if --days_test was
specified. According to the parameter description, --days_test is a
parameter to specify when the simulation should stop (days after
training). The simulator wants the start and end date in this format:
YYYYMMDDhhmm, which was not the case, thus the simulator wasn't
running properly. Now if the user specifies dates it works properly.

Example: ./zenbot.sh train binance.ETH-BTC --start_training 2018-01-01
--end_training 2018-01-03 --days_test 3

In this example, the training stops on Jan 2nd (midnight).
The simulation test runs after the period used in the training, thus
begins on on Jan 3rd and stops 3 days later, on Jan 5th (midnight).