colorbar shows itself after user switches the color variable

[Angus Yeh]

After use switched colorbar to be invisible, it will turn itself on again when color variable is switched.

[Angus Yeh]

Fix issue #99 colorbar shows itself after user switches the color variable.

Now by default hide colorbar when switching to No Fill. If user use combobox to show/hide other variable, the setting will be persistent. Ni Fill's setting will never affect other variables.

→ <<cset 38c223071ae0>>