Feature request: Ability to resize the sites list column

[robeastwood]

When viewing the sites panel, your list of sites might include some with long names.
Becuase the width of the column is fixed, you cannot read the full name.

On large screens, this is a missed opportunity - please can you allow the column to be resisable?

I think this maybe could be part of a wider effort to make the UI more customisable. eg:
#717