Add a wider V/C range.

[xujunhao6082]

According to #635, this request add a wider V/C range for creative source.
It has been tested

Implement Details

This is implemented through using int as a structure recording both order of magnitude (low 2 bits) and specific value.
(It maybe a C-style trick.)

[xujunhao6082]

There may be a downward compatibility issue caused by changes in data format.
But it is just a display issue, because the parameters of voltage/current sources are saved independently of the slider.