NB Power forecasts broken with the change back to standard time

[r24mille]

Here I thought "AD" in the .csv data meant "Anno Domini" and the timestamp was overly-specific about being after the the year 0. Here's a snippet of the problem from http://tso.nbpower.com/reports%20%26%20assessments/load%20forecast/hourly/2017-11-05%2001.csv

20171105000000AD,1293,0
20171105010000AD,1266,0
20171105010000AS,1261,0
20171105030000AS,1262,0

Turns out "AD" indicates "Atlantic Daylight Time" and "AS" indicates "Atlantic Standard Time" but including the letter "T" was deemed unnecessary by NB Power.

Fix NBPowerClient and add new unit tests for:

• time range entirely in daylight saving time
• time range of transition into daylight saving time
• time range entirely in standard time
• time range of transition into standard time