Improve handling of table column widths

The Volume column in Positions tab of Signal Bot can be initially truncated on the left of the value on 1920x1080 screen and require manual adjustment of the column widths. The column widths aren't remembered so they it needs to be done every time page is refreshed.

For example:
So "498.466968 USDT" appears as "198.466968 USDT" as the left side of the first digit has become cut off.

Possible improvements:
- Improve default columns widths so text isn't truncated
- Elliding text if the entire text can't be displayed in the column (e.g. "498.466968 USDT" becomes "498.466968 ...")