solving tps title always shows a time range of 1970-01-01 - 1970-01-01

Closes #233 (closed)

pass min_x, max_x to TimePowerSquaredWidget's plot_channels() to retrieve correct time for the plotting's title

With this fix, it help highlight zoom markers at the beginning and at the end of the data in the first plotting. (Before this fix, the markers are always in the wrong position in the first plot)