Fix the bug that time differs by 1 hour from the selected when BST/DS…

…T clocks change

[fix #462]

Before this commit the time calculated by the plugin was one hour more
than the time selected by the user when the clocks move forward an hour
and one hour less when the clocks move back for users in BST/DST regions.

This happened because to calculate the selected time, the selected hours
were added to the beginning of the selected day. For example, when user
selected 02:00 on the day when the clocks move forward then the calculated
time was 03:00 because the beginning of the day plus 2 hours is 03:00.
This is due to the fact that at 01:00 the clocks move forward an hour.

For more details see
https://en.wikipedia.org/wiki/British_Summer_Time
https://en.wikipedia.org/wiki/Daylight_saving_time

In this commit the code was changed to use the hour/minute MomentJS
functions to set time:

https://momentjs.com/docs/#/get-set/hour
https://momentjs.com/docs/#/get-set/minute