Make dock dots scalable

Make dock dots scalable

This patch makes the three dots in the dock change their size when bigger icon size is used.
The logic here is such that the dots are scaled only when a certain icon size is reached;
for instance, the dots will remain unchanged if icon size is less than 128x128 px, and will
be twice as big if it's set to a value from 128x128 to 184x184 px. The get_dot_mult() func
calculates and returns the scale multiplier. In the draw_dot() func, XDrawLine() and
XDrawPoint() were replaced with XFillRectangle() because those funcs do not allow their
result to be scalable. This patch does not require additional icon size values (those bigger
than 96x96 px) to exist, but makes no use without them.