Web Inspector: convert breakpoints to have a tri-state 'mode'.

The mode can be 'enabled', 'autocontinue', or 'disabled'. The UI
reflects these different modes with opacity settings. Clicking the
breakpoint markers will cycle between these modes.

The auto-continue mode only makes sense if there are actions
to evaluate, otherwise there is no effect from hitting. So, cycling
will not go to the auto-continue state unless the breakpoint has
actions.

Lastly, the breakpoint edit popover hides auto-continue when there
are no actions added for the breakpoint.
Probes: obtain and pass breakpoint action identifier to backend.
Probes: collect probe samples and send them through to the frontend.
Probes WIP - rename group to set, remove dead code
WIP probe manager