Add Turbolinks.enableScripts and .disableScripts. When disabled, scripts don't execute on executeScriptTags.

When executeScriptTags runs, it can re-attach events that need not be re-attached, e.g. when using jQuery .on() at the document level.

One can entirely avoid the need to re-execute scripts by using a combination of delegated events and Turbolinks' own page: events. With this change, one only needs to call Turbolinks.disableScripts() to avoid e.g. duplicating their events with every page:change.