Adds support for autoclick behavior:
- Adds new `autoclick` behavior option to `--behaviors`, but not
enabling by default
- Adds support for new exposed function `__bx_addSet` which allows
autoclick behavior to persist state about links that have already been
clicked to avoid duplicates, only used if link has an href
- Adds a new pageFinished flag on the worker state.
- Adds a on('dialog') handler to reject onbeforeunload page navigations,
when in behavior (page not finished), but accept when page is finished -
to allow navigation away only when behaviors are done
- Update to browsertrix-behaviors 0.7.0, which supports autoclick
- Add --clickSelector option to customize elements that will be clicked,
defaulting to `a`.
- Add --linkSelector as alias for --selectLinks for consistency
- Unknown options for --behaviors printed as warnings, instead of hard
exit, for forward compatibility for new behavior types in the future
Fixes#728, also #216, #665, #31
