4525: remove stale clippy code
4525: add test to verify selection on tab switching.
4525: Call enable_disable_selection_actions once per container to
avoid crosstalk between containers.

Also, separate event binding setup from enable/disable hook, and avoid
binding many copies of the selection dispatch click handler.
4525: restore add_form_selection_sources function
Merge branch '4525-remove-stale-clippy-code-TC' into 4525-remove-stale-clippy-code
4525: remove select_form_sources function
Merge branch 'master' into 4525-remove-stale-clippy-code
4525: remove add_form_selection_sources (one more time) and all references.
4525: keep link_to in application_helper, which will be used when attr value is a String or Fixnum etc
4525: link_to to be used when dataclass is a String or Fixnum
4525: delete assets/stylesheets/selection.css
4525: when dataclass is Class, return attrvalue similar to the Array case.
closes #4525
closes #4694
Merge branch '4525-remove-stale-clippy-code'