typo
Hovering over the code pane highlites the whole row

Including the line number, not just the code
Change mouse pointer over line numbers

Breakable lines get the clickable hand pointer, unbreakable get the default
pointer
function accepts optional code pane to limit its search

This lets us update one particular code pane or all of them
extract function to mark up code pane line numbers for breakpoints
Indicate breakpoints/actions when a new code pane is drawn

When a new codepane is created for a stack tab or opened file, mark every
line number that has a breakpoint or action